Stigma (letter) 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 used as a numeral symbol for the number 6. In this unrelated function, it is a continuation of the old letter digamma (originally Ϝ, cursive form ), which had served as a numeral since antiquity and was conflated with the σ-τ ligature in the minuscule handwriting of the Middle Ages. The στ ligature (, ) was one of many ligature forms that came into widespread use as
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