Variant Letters
In catering to the fine points of mathematical typesetting and notational clarity, the Wolfram Language provides a variety of special variant forms of letters.
Wolfram Language Notation and Doubled Letters
 \[ImaginaryI] — special form of  representing
 representing  (entered as
 (entered as  ii
ii )
)
 \[ConstantC] ▪  \[DifferentialD] ▪  \[ExponentialE] ▪  \[ImaginaryJ]
 \[DoubledGamma] ▪  \[DoubledPi]
Special Letter-Based Forms
µ \[Micro] ▪ Å \[Angstrom] ▪ ℏ \[HBar] ▪ ℘ \[WeierstrassP]
Variant Greek Letters
ε \[CurlyEpsilon] ▪ ϑ \[CurlyTheta] ▪ ϰ \[CurlyKappa] ▪ ϖ \[CurlyPi] ▪ ϱ \[CurlyRho] ▪ ς \[FinalSigma] ▪ φ \[CurlyPhi] ▪ ϒ \[CurlyCapitalUpsilon]
Dotless Letters
ı \[DotlessI] — dotless i, used for unit vectors with hats, etc.