Atomic sentence
In propositional calculus and in predicate calculus, an atomic formula (or simply atom) is either a propositional letter or an n-place predicate letter followed by n variables. An atomic sentence is the same as above except that the n-place predicate letter is followed by n constants or functors.
As examples, let P, M, T be predicate letters; let a, b, c, etc. be constant terms; but let x, y, z be variable terms; and let p be a propositional letter. Then these are atomic sentences:
- p
- M(a)
- P2(b,a,c)
but these are not atomic sentences (because there are free occurrences of variables):
- M(x)
- T(a,z)
- P2(x,y,z)