# 4

(Redirected from 4 (number))

 ← 3 4 5 →
Cardinalfour
Ordinal4th
(fourth)
Numeral systemquaternary
Factorization22
Divisors1, 2, 4
Greek numeralΔ´
Roman numeralIV, iv
Greek prefixtetra-
Binary1002
Ternary113
Senary46
Octal48
Duodecimal412
Arabic, Kurdish٤
Persian, Sindhi۴
Shahmukhi, Urdu۴
Ge'ez
Bengali, Assamese
Chinese numeral四，亖，肆
Devanagari
Telugu
Malayalam
Tamil
Hebrewד
Khmer
Thai
Burmese

4 (four) is a number, numeral and digit. It is the natural number following 3 and preceding 5. It is the smallest semiprime and composite number, and is considered unlucky in many East Asian cultures.

## In mathematics

Four is the smallest composite number, its proper divisors being 1 and 2.[1] Four is the sum and product of two with itself: ${\displaystyle 2}$ + ${\displaystyle 2}$ = ${\displaystyle 4}$ = ${\displaystyle 2}$ x ${\displaystyle 2}$, the only number ${\displaystyle b}$ such that ${\displaystyle a}$ + ${\displaystyle a}$ = ${\displaystyle b}$ = ${\displaystyle a}$ x ${\displaystyle a}$, which also makes four the smallest squared prime number ${\displaystyle p^{2}}$. In Knuth's up-arrow notation, 2 ↑↑ 2 = 2 ↑↑↑ 2 = 4, and so forth, for any number of up arrows.[2] By consequence, four is the only square one more than a prime number, specifically three. The sum of the first four prime numbers two + three + five + seven is the only sum of four consecutive prime numbers that yields an odd prime number, seventeen, which is the fourth super-prime. Four lies between the first proper pair of twin primes, three and five, which are the first two Fermat primes, like seventeen, which is the third. On the other hand, the square of four 42, equivalently the fourth power of two 24, is sixteen; the only number that has ${\displaystyle a^{b}}$ = ${\displaystyle b^{a}}$ as a form of factorization. Holistically, there are four elementary arithmetic operations in mathematics: addition (+), subtraction (), multiplication (×), and division (÷); and four basic number systems, the real numbers ${\displaystyle \mathbb {R} }$, rational numbers ${\displaystyle \mathbb {Q} }$, integers ${\displaystyle \mathbb {Z} }$, and natural numbers ${\displaystyle \mathbb {N} }$.

Each natural number divisible by 4 is a difference of squares of two natural numbers, i.e. ${\displaystyle 4x}$ = ${\displaystyle y^{2}}$${\displaystyle z^{2}}$. A number is a multiple of 4 if its last two digits are a multiple of 4.[3] For example, 1092 is a multiple of 4 because 92 = 4 × 23.

Lagrange's four-square theorem states that every positive integer can be written as the sum of at most four square numbers.[4] Three are not always sufficient; 7 for instance cannot be written as the sum of three squares.[5]

There are four all-Harshad numbers: 1, 2, 4, and 6. 12, which is divisible by four thrice over, is a Harshad number in all bases except octal.

A four-sided plane figure is a quadrilateral or quadrangle, sometimes also called a tetragon. It can be further classified as a rectangle or oblong, kite, rhombus, and square.

Four is the highest degree general polynomial equation for which there is a solution in radicals.[6]

The four-color theorem states that a planar graph (or, equivalently, a flat map of two-dimensional regions such as countries) can be colored using four colors, so that adjacent vertices (or regions) are always different colors.[7] Three colors are not, in general, sufficient to guarantee this.[8] The largest planar complete graph has four vertices.[9]

A solid figure with four faces as well as four vertices is a tetrahedron, which is the smallest possible number of faces and vertices a polyhedron can have.[10][11] The regular tetrahedron, also called a 3-simplex, is the simplest Platonic solid.[12] It has four regular triangles as faces that are themselves at dual positions with the vertices of another tetrahedron.[13] Tetrahedra can be inscribed inside all other four Platonic solids, and tessellate space alongside the regular octahedron in the alternated cubic honeycomb.

Four-dimensional space is the highest-dimensional space featuring more than three regular convex figures:

The fourth dimension is also the highest dimension where regular self-intersecting figures exist:

Altogether, sixteen (or 16 = 42) regular convex and star polychora are generated from symmetries of four (4) Coxeter Weyl groups and point groups in the fourth dimension: the ${\displaystyle \mathrm {A} _{4}}$ simplex, ${\displaystyle \mathrm {B} _{4}}$ hypercube, ${\displaystyle \mathrm {F} _{4}}$ icositetrachoric, and ${\displaystyle \mathrm {H} _{4}}$ hexacosichoric groups; with the ${\displaystyle \mathrm {D} _{4}}$ demihypercube group generating two alternative constructions.

There are also sixty-four (or 64 = 43) four-dimensional Bravais lattices, and sixty-four uniform polychora in the fourth dimension based on the same ${\displaystyle \mathrm {A} _{4}}$, ${\displaystyle \mathrm {B} _{4}}$, ${\displaystyle \mathrm {F} _{4}}$ and ${\displaystyle \mathrm {H} _{4}}$ Coxeter groups, and extending to prismatic groups of uniform polyhedra, including one special non-Wythoffian form, the grand antiprism. There are also two infinite families of duoprisms and antiprismatic prisms in the fourth dimension.

Four-dimensional differential manifolds have some unique properties. There is only one differential structure on ${\displaystyle \mathbb {R} ^{n}}$ except when ${\displaystyle n}$ = ${\displaystyle 4}$, in which case there are uncountably many.

The smallest non-cyclic group has four elements; it is the Klein four-group.[14] An alternating groups are not simple for values ${\displaystyle n}$${\displaystyle 4}$.

Further extensions of the real numbers under Hurwitz's theorem states that there are four normed division algebras: the real numbers ${\displaystyle \mathbb {R} }$, the complex numbers ${\displaystyle \mathbb {C} }$, the quaternions ${\displaystyle \mathbb {H} }$, and the octonions ${\displaystyle \mathbb {O} }$. Under Cayley–Dickson constructions, the sedenions ${\displaystyle \mathbb {S} }$ constitute a further fourth extension over ${\displaystyle \mathbb {R} }$. The real numbers are ordered, commutative and associative algebras, as well as alternative algebras with power-associativity. The complex numbers ${\displaystyle \mathbb {C} }$ share all four multiplicative algebraic properties of the reals ${\displaystyle \mathbb {R} }$, without being ordered. The quaternions loose a further commutative algebraic property, while holding associative, alternative, and power-associative properties. The octonions are alternative and power-associative, while the sedenions are only power-associative. The sedenions and all further extensions of these four normed division algebras are solely power-associative with non-trivial zero divisors, which makes them non-division algebras. ${\displaystyle \mathbb {R} }$ has a vector space of dimension 1, while ${\displaystyle \mathbb {C} }$, ${\displaystyle \mathbb {H} }$, ${\displaystyle \mathbb {O} }$ and ${\displaystyle \mathbb {S} }$ work in algebraic number fields of dimensions 2, 4, 8, and 16, respectively.

## List of basic calculations

Multiplication 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 50 100 1000
4 × x 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 64 68 72 76 80 84 88 92 96 100 200 400 4000
Division 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
4 ÷ x 4 2 1.3 1 0.8 0.6 0.571428 0.5 0.4 0.4 0.36 0.3 0.307692 0.285714 0.26 0.25
x ÷ 4 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5 2.75 3 3.25 3.5 3.75 4
Exponentiation 1 2 3 4 5 6 7 8 9 10 11 12 13
4x 4 16 64 256 1024 4096 16384 65536 262144 1048576 4194304 16777216 67108864
x4 1 16 81 256 625 1296 2401 4096 6561 10000 14641 20736 28561

## Evolution of the Hindu-Arabic digit

Two modern handwritten fours

Brahmic numerals represented 1, 2, and 3 with as many lines. 4 was simplified by joining its four lines into a cross that looks like the modern plus sign. The Shunga would add a horizontal line on top of the digit, and the Kshatrapa and Pallava evolved the digit to a point where the speed of writing was a secondary concern. The Arabs' 4 still had the early concept of the cross, but for the sake of efficiency, was made in one stroke by connecting the "western" end to the "northern" end; the "eastern" end was finished off with a curve. The Europeans dropped the finishing curve and gradually made the digit less cursive, ending up with a digit very close to the original Brahmin cross.[15]

While the shape of the character for the digit 4 has an ascender in most modern typefaces, in typefaces with text figures the glyph usually has a descender, as, for example, in .

On the seven-segment displays of pocket calculators and digital watches, as well as certain optical character recognition fonts, 4 is seen with an open top.[16]

Television stations that operate on channel 4 have occasionally made use of another variation of the "open 4", with the open portion being on the side, rather than the top. This version resembles the Canadian Aboriginal syllabics letter ᔦ. The magnetic ink character recognition "CMC-7" font also uses this variety of "4".[17]

## In politics

• Four Freedoms: four fundamental freedoms that Franklin D. Roosevelt declared ought to be enjoyed by everyone in the world: Freedom of Speech, Freedom of Religion, Freedom from Want, Freedom from Fear.[59]
• Gang of Four: Popular name for four Chinese Communist Party leaders who rose to prominence during China's Cultural Revolution, but were ousted in 1976 following the death of Chairman Mao Zedong. Among the four was Mao's widow, Jiang Qing. Since then, many other political factions headed by four people have been called "Gangs of Four".[60]

## In science

### In chemistry

• Valency of carbon (that is basis of life on the Earth) is four. Also because of its tetrahedral crystal bond structure, diamond (one of the natural allotropes of carbon) is the hardest known naturally occurring material. It is also the valence of silicon, whose compounds form the majority of the mass of the Earth's crust.[75]
• The atomic number of beryllium[76]
• There are four basic states of matter: solid, liquid, gas, and plasma.[77]

## In logic and philosophy

Four mugs
• The symbolic meanings of the number four are linked to those of the cross and the square. "Almost from prehistoric times, the number four was employed to signify what was solid, what could be touched and felt. Its relationship to the cross (four points) made it an outstanding symbol of wholeness and universality, a symbol which drew all to itself". Where lines of latitude and longitude intersect, they divide the earth into four proportions. Throughout the world kings and chieftains have been called "lord of the four suns" or "lord of the four quarters of the earth",[81] which is understood to refer to the extent of their powers both territorially and in terms of total control of their subjects' doings.
• The Square of Opposition, in both its Aristotelian version and its Boolean version, consists of four forms: A ("All S is R"), I ("Some S is R"), E ("No S is R"), and O ("Some S is not R").
• In regard to whether two given propositions can have the same truth value, there are four separate logical possibilities: the propositions are subalterns (possibly both are true, and possibly both are false); subcontraries (both may be true, but not that both are false); contraries (both may be false, but not that both are true); or contradictories (it is not possible that both are true, and it is not possible that both are false).
• Aristotle held that there are basically four causes in nature: the material, the formal, the efficient, and the final.[82]
• The Stoics held with four basic categories, all viewed as bodies (substantial and insubstantial): (1) substance in the sense of substrate, primary formless matter; (2) quality, matter's organization to differentiate and individualize something, and coming down to a physical ingredient such as pneuma, breath; (3) somehow holding (or disposed), as in a posture, state, shape, size, action, and (4) somehow holding (or disposed) toward something, as in relative location, familial relation, and so forth.
• Immanuel Kant expounded a table of judgments involving four three-way alternatives, in regard to (1) Quantity, (2) Quality, (3) Relation, (4) Modality, and, based thereupon, a table of four categories, named by the terms just listed, and each with three subcategories.
• Arthur Schopenhauer's doctoral thesis was On the Fourfold Root of the Principle of Sufficient Reason.
• Franz Brentano held that any major philosophical period has four phases: (1) Creative and rapidly progressing with scientific interest and results; then declining through the remaining phases, (2) practical, (3) increasingly skeptical, and (4) literary, mystical, and scientifically worthless—until philosophy is renewed through a new period's first phase. (See Brentano's essay "The Four Phases of Philosophy and Its Current State" 1895, tr. by Mezei and Smith 1998.)
• C. S. Peirce, usually a trichotomist, discussed four methods for overcoming troublesome uncertainties and achieving secure beliefs: (1) the method of tenacity (policy of sticking to initial belief), (2) the method of authority, (3) the method of congruity (following a fashionable paradigm), and (4) the fallibilistic, self-correcting method of science (see "The Fixation of Belief", 1877); and four barriers to inquiry, barriers refused by the fallibilist: (1) assertion of absolute certainty; (2) maintaining that something is unknowable; (3) maintaining that something is inexplicable because absolutely basic or ultimate; (4) holding that perfect exactitude is possible, especially such as to quite preclude unusual and anomalous phenomena (see "F.R.L." [First Rule of Logic], 1899).
• Paul Weiss built a system involving four modes of being: Actualities (substances in the sense of substantial, spatiotemporally finite beings), Ideality or Possibility (pure normative form), Existence (the dynamic field), and God (unity). (See Weiss's Modes of Being, 1958).
• Karl Popper outlined a tetradic schema to describe the growth of theories and, via generalization, also the emergence of new behaviors and living organisms: (1) problem, (2) tentative theory, (3) (attempted) error-elimination (especially by way of critical discussion), and (4) new problem(s). (See Popper's Objective Knowledge, 1972, revised 1979.)
• John Boyd (military strategist) made his key concept the decision cycle or OODA loop, consisting of four stages: (1) observation (data intake through the senses), (2) orientation (analysis and synthesis of data), (3) decision, and (4) action.[83] Boyd held that his decision cycle has philosophical generality, though for strategists the point remains that, through swift decisions, one can disrupt an opponent's decision cycle.
• Richard McKeon outlined four classes (each with four subclasses) of modes of philosophical inquiry: (1) Modes of Being (Being); (2) Modes of Thought (That which is); (3) Modes of Fact (Existence); (4) Modes of Simplicity (Experience)—and, corresponding to them, four classes (each with four subclasses) of philosophical semantics: Principles, Methods, Interpretations, and Selections. (See McKeon's "Philosophic Semantics and Philosophic Inquiry" in Freedom and History and Other Essays, 1989.)
• Jonathan Lowe (E.J. Lowe) argues in The Four-Category Ontology, 2006, for four categories: kinds (substantial universals), attributes (relational universals and property-universals), objects (substantial particulars), and modes (relational particulars and property-particulars, also known as "tropes"). (See Lowe's "Recent Advances in Metaphysics," 2001, Eprint)
• Four opposed camps of the morality and nature of evil: moral absolutism, amoralism, moral relativism, and moral universalism.

## In technology

4 as a resin identification code, used in recycling

## In sports

• In the Australian Football League, the top level of Australian rules football, each team is allowed 4 "interchanges" (substitute players), who can be freely substituted at any time, subject to a limit on the total number of substitutions.
• In baseball:
• There are four bases in the game: first base, second base, third base, and home plate; to score a run, an offensive player must complete, in the sequence shown, a circuit of those four bases.
• When a batter receives four pitches that the umpire declares to be "balls" in a single at-bat, a base on balls, informally known as a "walk", is awarded, with the batter sent to first base.
• For scoring, number 4 is assigned to the second baseman.
• Four is the most runs that can be scored on any single at bat, whereby all three baserunners and the batter score (the most common being via a grand slam).
• The fourth batter in the batting lineup is called the cleanup hitter.
• In basketball, the number four is used to designate the power forward position, often referred to as "the four spot" or "the four".[90]
• In cricket, a four is a specific type of scoring event, whereby the ball crosses the boundary after touching the ground at least one time, scoring four runs. Taking four wickets in four consecutive balls is typically referred to as a double hat trick (two consecutive, overlapping hat tricks).
• In American Football teams get four downs to reach the line of gain.
• In rowing, a four refers to a boat for four rowers, with or without coxswain. In rowing nomenclature, 4− represents a coxless four and 4+ represents a coxed four.
• In rugby league:
• A try is worth 4 points.
• One of the two starting centres wears the jersey number 4. (An exception to this rule is the Super League, which uses static squad numbering.)
• In rugby union:
• One of the two starting locks wears the jersey number 4.
• In the standard bonus points system, a point is awarded in the league standings to a team that scores at least 4 tries in a match, regardless of the match result.

## References

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5. ^ Peterson, Ivars (2002). Mathematical Treks: From Surreal Numbers to Magic Circles. MAA. p. 95. ISBN 978-0-88385-537-9. 7 is an example of an integer that can't be written as the sum of three squares.
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8. ^ Ben-Menahem, Ari (6 March 2009). Historical Encyclopedia of Natural and Mathematical Sciences. Springer Science & Business Media. p. 2147. ISBN 978-3-540-68831-0. (i.e. That there are maps for which three colors are not sufficient)
9. ^ Molitierno, Jason J. (19 April 2016). Applications of Combinatorial Matrix Theory to Laplacian Matrices of Graphs. CRC Press. p. 197. ISBN 978-1-4398-6339-8. ... The complete graph on the largest number of vertices that is planar is K4 and that a(K4) equals 4.
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13. ^ Hilbert, David; Cohn-Vossen, Stephan (1999). Geometry and the Imagination. American Mathematical Soc. p. 143. ISBN 978-0-8218-1998-2. ...the tetrahedron plays an anomalous role in that it is self-dual, whereas the four remaining polyhedra are mutually dual in pairs...
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29. ^ Stevenson, Kenneth; Glerup, Michael (19 March 2014). Ezekiel, Daniel. InterVarsity Press. pp. xlv. ISBN 978-0-8308-9738-4. We have already mentioned the four living creatures—the man, the lion, the ox and the eagle
30. ^ Butnick, Stephanie; Leibovitz, Liel; Oppenheimer, Mark (1 October 2019). The Newish Jewish Encyclopedia: From Abraham to Zabar's and Everything in Between. Artisan Books. ISBN 978-1-57965-893-9. ...be like Sarah, Rachel, Rebecca, and Leah, the foremothers of Judaism
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39. ^ Maanas - Individual and Society. Rapid Publications. ISBN 978-1-937192-06-8. The Four Stages of Life
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44. ^ Çakmak, Cenap (18 May 2017). Islam: A Worldwide Encyclopedia [4 volumes]. ABC-CLIO. p. 397. ISBN 978-1-61069-217-5. ...Eid al-Adha (Feast of Sacrifice) lasts four days ...
45. ^ Leonard, Timothy; Willis, Peter (11 June 2008). Pedagogies of the Imagination: Mythopoetic Curriculum in Educational Practice. Springer Science & Business Media. p. 144. ISBN 978-1-4020-8350-1. ... four Rightly Guided Caliphs, Abu-Bakr, Umar ibn al-Khattab, Uthman ibn Affan and Ali ibn Abi Talib,...
46. ^ Chwalkowski, Farrin (14 December 2016). Symbols in Arts, Religion and Culture: The Soul of Nature. Cambridge Scholars Publishing. p. 23. ISBN 978-1-4438-5728-4. According to Islam, the Four Arch Angels are: Jibraeel (Gabriel), Mikaeel (Michael), Izraeel (Azrael), and Israfil (Raphael).
47. ^ Busool, Assad Nimer (28 December 2010). The Wise Qur'an: These are the Verses of the Wise Book: These are the verses of the Wise Book. Xlibris Corporation. p. 50. ISBN 978-1-4535-2526-5. The sacred months are four, Rajab, Dhu al-Qi'dah, Dhu al-Hijjah, and al-Muharram. During those four sacred months there were no war...
48. ^ Shabazz, Hassan (6 January 2020). Al Islaam, and the Transformation of Society. Lulu.com. p. 15. ISBN 978-1-7948-3337-1. There are four books in Islam: Torah, Zaboor, Injeel and Holy Qur'an...
49. ^ Bukhari, Muohammad Ben Ismail Al (1 January 2007). THE CORRECT TRADITIONS OF AL'BUKHARI 1-4 VOL 3: صحيح البخاري 1/4 [عربي/انكليزي] ج3. Dar Al Kotob Al Ilmiyah دار الكتب العلمية. p. 840. For those who take an oath for abstention from their wives, awaiting for four months is ordained;
50. ^ Ahmad, Yusuf Al-Hajj. The Book Of Nikkah: Encyclopaedia of Islamic Law. Darussalam Publishers. ...for four months and ten days.
51. ^ Mawdudi, Sayyid Abul A'la (15 December 2016). Towards Understanding the Qur'an: English Only Edition. Kube Publishing Ltd. p. 59. ISBN 978-0-86037-613-2. Then take four birds, ...
52. ^ Maudoodi, Syed Abul ʻAla (2000). Sūrah al-Aʻarāf to Sūrah bani Isrāel. Islamic Publications. p. 177. The respite of four months...
53. ^ Barazangi, Nimat Hafez (9 March 2016). Woman's Identity and Rethinking the Hadith. Routledge. p. 138. ISBN 978-1-134-77065-6. And those who launch a charge against chaste women and do not produce four witnesses...
54. ^ SK, Lim. Origins of Chinese Auspicious Symbols. Asiapac Books Pte Ltd. p. 16. ISBN 978-981-317-026-1. Taoism later incorporated the four symbols into its immortality system...
55. ^ Terry, Milton Spenser (1883). Biblical Hermenutics: A Treatise on the Interpretation of the Old and New Testaments. Phillips & Hunt. p. 382. the four corners or extremities of the earth (Isa. xi, 12; Ezek. vii, 2.; Rev. vii, 1 ; xx, 8), corresponding, doubtless, with the four points of the compass
56. ^ Bulletin - State Department of Education. Department of Education. 1955. p. 151. Four was a sacred number of Zia
57. ^ Lachenmeyer, Nathaniel (2005). 13: The Story of the World's Most Notorious Superstition. Penguin Group (USA) Incorporated. p. 187. ISBN 978-0-452-28496-8. In Chinese , Japanese , and Korean , the word for four is , unfortunately , an exact homonym for death
58. ^ Maberry, Jonathan; Kramer, David F. (2007). The Cryptopedia: A Dictionary of the Weird, Strange & Downright Bizarre. Citadel Press. p. 211. ISBN 978-0-8065-2819-9. Svetovid is portrayed as having four heads ...
59. ^ "FDR, 'The Four Freedoms,' Speech Text". Voices of Democracy. Retrieved 30 July 2020.
60. ^ "Yao Wenyuan". The Economist. ISSN 0013-0613. Retrieved 30 July 2020.
61. ^ Raphael, Howard A., ed. (November 1974). "The Functions Of A Computer: Instruction Register And Decoder" (PDF). MCS-40 User's Manual For Logic Designers. Santa Clara, California, USA: Intel Corporation. p. viii. Archived (PDF) from the original on 3 March 2020. Retrieved 3 March 2020. [...] The characteristic eight bit field is sometimes referred to as a byte, a four bit field can be referred to as a nibble. [...]
62. ^ Petsko, Gregory A.; Ringe, Dagmar (2004). Protein Structure and Function. New Science Press. p. 40. ISBN 978-0-87893-663-2. Oligomers containing two, three, four, five, six or even more subunits are known as dimers, trimers, tetramers, pentamers, hexamers, and so on.
63. ^ Yaqoob, Tahir (2011). Exoplanets and Alien Solar Systems. New Earth Labs. p. 12. ISBN 978-0-9741689-2-0. The four inner planets (known as terrestrial, or rocky planets
64. ^ Encrenaz, Therese; Bibring, Jean-Pierre; Blanc, M.; Barucci, Maria-Antonietta; Roques, Francoise; Zarka, Philippe (26 January 2004). The Solar System. Springer Science & Business Media. p. 283. ISBN 978-3-540-00241-3. ...the gas giants (Jupiter and Saturn), and the icy giants (Uranus and Neptune)
65. ^ Pidwirny, Michael (7 May 2020). Chapter 3: Matter, Energy and the Universe: Single chapter from the eBook Understanding Physical Geography. Our Planet Earth Publishing. p. 10. including the four large Galilean moons that are easily visible from a hobby telescope
66. ^ Pugh, Philip (2 November 2011). Observing the Messier Objects with a Small Telescope: In the Footsteps of a Great Observer. Springer Science & Business Media. p. 41. ISBN 978-0-387-85357-4. M4 is a globular star cluster near Antares in Scorpius.
67. ^ Bok, Bart Jan; Bok, Priscilla Fairfield (1981). The Milky Way. Harvard University Press. p. 66. ISBN 978-0-674-57503-5. IV , subgiants
68. ^ Encyclopedia of Cell Biology. Academic Press. 7 August 2015. p. 25. ISBN 978-0-12-394796-3.
69. ^ Chien, Shu; Chen, Peter C. Y.; Fung, Yuan-cheng (2008). An Introductory Text to Bioengineering. World Scientific. p. 54. ISBN 978-981-270-793-2. The mammalian heart consists of four chambers,...
70. ^ Creation Research Society Textbook Committee (1970). Biology: a search for order in complexity. Zondervan Pub. House. p. 209. ISBN 978-0-310-29490-0. Except for the flies, mosquitoes, and some others, insects with wings have four wings.
71. ^ Pittenger, Dennis (15 December 2014). California Master Gardener Handbook, 2nd Edition. UCANR Publications. p. 180. ISBN 978-1-60107-857-5. metamorphosis is marked by four distinct stages
72. ^ Darpan, Pratiyogita (2008). Pratiyogita Darpan. Pratiyogita Darpan. p. 85. In the 'ABO' system, all blood belongs one of four major groups — A, B, AB or O
73. ^ Daniels, Patricia; Stein, Lisa (2009). Body: The Complete Human : how it Grows, how it Works, and how to Keep it Healthy and Strong. National Geographic Books. p. 94. ISBN 978-1-4262-0449-4. Four canines for tearing + Eight premolars for crushing +Twelve molars (including four wisdom teeth)
74. ^ Woodward, Thompson Elwyn; Nystrom, Amer Benjamin (1930). Feeding Dairy Cows. U.S. Department of Agriculture. p. 4. The cow's stomach is divided into four compartments.
75. ^ Lucas, Jerry (1993). Great unsolved mysteries of science. F & W Pubns Inc. p. 168. ISBN 978-1-55870-291-2. Of course, carbon is not the only chemical element with a valence of +4 or -4
76. ^ Walsh, Kenneth A. (1 January 2009). Beryllium Chemistry and Processing. ASM International. p. 93. ISBN 978-0-87170-721-5. Beryllium has an atomic number of four
77. ^ Ebeling, Werner; Fortov, Vladimir E.; Filinov, Vladimir (27 November 2017). Quantum Statistics of Dense Gases and Nonideal Plasmas. Springer. p. 39. ISBN 978-3-319-66637-2. Plasma is one of the four fundamental states of matter, the others being solid, liquid, and gas.
78. ^ Petkov, Vesselin (23 June 2009). Relativity and the Nature of Spacetime. Springer Science & Business Media. p. 124. ISBN 978-3-642-01962-3. should be regarded as a four-dimensional world
79. ^ Giordano, Nicholas (13 February 2009). College Physics: Reasoning and Relationships. Cengage Learning. p. 1073. ISBN 978-0-534-42471-8. We have referred to the four fundamental forces in nature,...
80. ^ Alon, Noga; Spencer, Joel H. (20 September 2011). The Probabilistic Method. John Wiley & Sons. p. 6.1. ISBN 978-1-118-21044-4. The Four Functions Theorem of Ahlswede Daykin
81. ^ Chevalier, Jean and Gheerbrant, Alain (1994), The Dictionary of Symbols. The quote beginning "Almost from prehistoric times..." is on p. 402.
82. ^ Hennig, Boris (5 December 2018). Aristotle's Four Causes. Peter Lang. ISBN 978-1-4331-5929-9. This book examines Aristotle's four causes (material, formal, efficient, and final)
83. ^ Wilkinson, Amy (17 February 2015). The Creator's Code: The Six Essential Skills of Extraordinary Entrepreneurs. Simon and Schuster. p. 79. ISBN 978-1-4516-6609-0. The OODA loop consists of four steps.
84. ^ Howard, Brian Clark; Abdelrahman, Amina Lake; Good Housekeeping Institute (26 February 2020). "You Might Be Recycling Wrong — Here's Everything You Need to Know About Recycling Symbols". Good Housekeeping. Retrieved 28 July 2020. Plastic Recycling Symbol #4: LDPE
85. ^ Conover, Charles (8 November 2011). Designing for Print. John Wiley & Sons. p. 62. ISBN 978-1-118-13088-9. CMYK is the standard four-color model used for all full-color print jobs that will be output on an offset printing press
86. ^ Vermaat, Misty E.; Sebok, Susan L.; Freund, Steven M.; Campbell, Jennifer T.; Frydenberg, Mark (1 January 2015). Discovering Computers, Essentials. Cengage Learning. p. 123. ISBN 978-1-305-53402-5. ...the 4 key (labeled with the letters g,h and i)...
87. ^ Bunting, Steve; Wei, William (6 March 2006). EnCase Computer Forensics: The Official EnCE: EnCase?Certified Examiner Study Guide. John Wiley & Sons. p. 246. ISBN 978-0-7821-4435-2. A byte also contains two 4-bit nibbles...
88. ^ Braden, R. "Requirements for Internet Hosts - Communication Layers". tools.ietf.org. pp. 9–10. Retrieved 28 July 2020.
89. ^ Assenza, Tony (June 1982). "Audi Quattro: Germany's 4x4 Cruise Missile". Popular Mechanics. Hearst Magazines.
90. ^ Schaller, Bob; Harnish, Dave (18 September 2009). The Everything Kids' Basketball Book: The all-time greats, legendary teams, today's superstars - and tips on playing like a pro. Simon and Schuster. ISBN 978-1-4405-0177-7. Power forward Referred to as the number 4 spot
91. ^ "Definition of FOUR-LETTER WORD". merriam-webster.com. Retrieved 28 July 2020.
92. ^ Wells, J. C. (25 September 2014). Sounds Interesting: Observations on English and General Phonetics. Cambridge University Press. p. 33. ISBN 978-1-316-12385-0. But one confused re-spelling is fower for 'four'.
93. ^ Guttman, Ariel; Guttman, Gail; Johnson, Kenneth (1993). Mythic Astrology: Archetypal Powers in the Horoscope. Llewellyn Worldwide. p. 263. ISBN 978-0-87542-248-0. Sign: Cancer, the fourth Zodiacal Sign
94. ^ Curtiss, Harriette A. (1996). The Key to the Universe. Health Research Books. p. 161. ISBN 978-0-7873-1233-6. The 4th Tarot Card is called "The Emperor."
95. ^ Weller, David; Lobao, Alexandre Santos; Hatton, Ellen (20 September 2004). Beginning .NET Game Programming in VB .NET. Apress. p. 383. ISBN 978-1-4302-0724-5. ...tetraminos (the shapes used in Tetris) are all just a collection of four blocks
96. ^ Jozefowicz, Chris (7 August 2009). Video Games. Gareth Stevens Publishing LLLP. p. 17. ISBN 978-1-4339-4406-2. Tetra means "four" in Greek. Blocks in the game are made of four squares
97. ^ Bardes, Barbara; Shelley, Mack; Schmidt, Steffen (16 December 2008). American Government and Politics Today: The Essentials 2009 - 2010 Edition. Cengage Learning. p. 453. ISBN 978-0-495-57170-4. The court will not issue a writ unless at least four justices approve of it. This is called the rule of four.
98. ^ "Movie Projector: 'I Am Number Four' to be No. 1 at holiday weekend box office [Updated]". LA Times Blogs - Company Town. 17 February 2011. Retrieved 28 July 2020.
99. ^ "fourth wall". dictionary.cambridge.org. Retrieved 29 November 2021.
100. ^ Roberts, Gareth E. (15 February 2016). From Music to Mathematics: Exploring the Connections. JHU Press. p. 3. ISBN 978-1-4214-1918-3. ... called common time and denoted by C, which has four beats per measure
101. ^ Bonds, Mark Evan (10 January 2009). Music as Thought: Listening to the Symphony in the Age of Beethoven. Princeton University Press. p. 1. ISBN 978-1-4008-2739-8. The number, character and sequence of movements in the symphony, moreover, did not stabilize until the 1770s when the familiar format of four movements...
102. ^ Frisch, Walter (2003). Brahms: The Four Symphonies. Yale University Press. ISBN 978-0-300-09965-2.
103. ^ Brech, Lewis (2010). Storybook Advent Carols Collection Songbook. Couples Company, Inc. p. 26. ISBN 978-1-4524-7763-3.
104. ^ Wright, Robert J.; Ellemor-Collins, David; Tabor, Pamela D. (4 November 2011). Developing Number Knowledge: Assessment,Teaching and Intervention with 7-11 year olds. SAGE. ISBN 978-1-4462-5368-7.
105. ^ Macauley, David (29 September 2010). Elemental Philosophy: Earth, Air, Fire, and Water as Environmental Ideas. SUNY Press. ISBN 978-1-4384-3246-5.
106. ^ Brooks, Edward (1876). Normal Higher Arithmetic Designed for Advanced Classes in Common Schools, Normal Schools, and High Schools, Academics, Etc. Sower. p. 227. Every year that is divisible by four, except the Centennial years, and every Centennial year divisible by 400, is a leap year...
107. ^ Touche, Fred; Price, Anne (2005). Wilderness Navigation Handbook. Touche Publishing. p. 48. ISBN 978-0-9732527-0-5. Each of the familiar cardinal directions is equivalent to a particular true bearing: north (0°), east (90°), south (180°), and west (270°)
108. ^ Roeckelein, J. E. (19 January 2006). Elsevier's Dictionary of Psychological Theories. Elsevier. p. 235. ISBN 978-0-08-046064-2. ...four substances or humors: blood, yellow bile, black bile and phlegm
109. ^ Medley, H. Anthony (1997). Bridge. Penguin. p. 6. ISBN 978-0-02-861735-0. The four playing card suits, as you probably already know, are spades, hearts, diamonds, and clubs
110. ^ Baker, Felicity (2017). Houses of Hogwarts: Cinematic Guide. Scholastic Incorporated. ISBN 978-1-338-12861-1. ...the four houses of Hogwarts School of Witchcraft and Wizardry: Gryffindor, Ravenclaw, Hufflepuff, and Slytherin