Stigma (letter) sigma form ς never occurs inside a word and is never used as a numeral either. Uppercase forms of stigma as a numeral (Ϛ) are rare in practice; when they occur, they can often be confused with uppercase forms of another numeral symbol, koppa (Ϟϟ), which stands for 90. Stigma is encoded in Unicode as "Greek letter stigma" U+03DA (Ϛ) and "Greek small letter stigma" U+03DB (ϛ). Stigma (letter) Stigma (ϛ) is a ligature of the Greek letters sigma (Σ) and tau (Τ), which was used in writing Greek between the Middle Ages and the 19th century. It is also
Mu (letter) monotonic orthography, the ancient version is written with an acute accent instead of a circumflex: . The lowercase letter mu (μ) is used as a special symbol in many academic fields. Uppercase mu is not used, because it appears identical to Latin M. "μ" is conventionally used to denote certain things; however, any Greek letter or other symbol may be used freely as a variable name. In classical physics and engineering: In particle physics: In thermodynamics: In evolutionary algorithms: In type theory: In chemistry: In biology: In pharmacology: In orbital mechanics: The Olympus Corporation manufactures a series of digital cameras