Kai is the most frequent word in any Greek text and thus used by statisticians to assess authorship of ancient manuscripts (see below).
Kai ligature 
Because of its frequent occurrence, kai is sometimes abbreviated in Greek manuscripts, by a ligature (comparable to Latin &, written as ϗ (uppercase variant Ϗ; Coptic variant ⳤ), formed from kappa (κ) with an extra lower stroke. It may occur with the varia above it: ϗ̀.
Authorship of ancient texts 
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The number of common words which express a general relation ("and", "in", "but", "I", "to be") is random with the same distribution at least among the same genre. By contrast, the occurrence of the definite article "the" cannot be modeled by simple probabilistic laws because the number of nouns with definite article depends on the subject matter.
Table 1 has data about the epistles of St. Paul. Abbreviations: Rom Romans; Co1 1st Corinthians; Co2 2nd Corinthians; Gal Galatians; Phi Philippians; Col Colossians; Th1 1st Thessalonians; Ti1 1st Timothy; Ti2 2nd Timothy; Heb Hebrews. 2nd Thessalonians, Titus, and Philemon were excluded because they were too short to give reliable samples. From an analysis of these and other data [Mor65, p. 224] the first 4 epistles (Romans, 1 Corinthians, 2 Corinthians, and Galatians) form a consistent group, and all the other epistles lie more than 2 standard deviations from the mean of this group (using statistics).
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- [Mor65] A. Q. Morton. The authorship of Greek prose (with discussion). Journal of the Royal Statistical Society, Series A, 128:169–233, 1965
This article incorporates material from Econ 7800 class notes by Hans G. Ehbar, which is licensed under GFDL
- Proposal to encode the uppercase letter in Danish