Greek letters are used in
mathematics,
science,
engineering, and other areas where mathematical notation is used as symbols for
constants,
special functions, and also conventionally for
variables representing certain quantities. In these contexts, the capital letters and the small letters represent distinct and unrelated entities. Those Greek letters which have the same form as
Latin letters are usually not used: capital A, B, E, H, I, K, M, N, O, P, T, X, Y, Z. Small ι (iota), ο (omicron) and υ (upsilon) are also rarely used, since they closely resemble the Latin letters i, o and u. Sometimes font variants of Greek letters are used as distinct symbols in mathematics, in particular for ε/ϵ (epsilon) and π/ϖ (pi). Additionally, despite being obsolete in Modern Greek, the archaic letter
digamma (Ϝ/ϝ/ϛ) is sometimes used.