Mathematical Script Small I

It marks a distinct variable; the equation decides what it stands for.

Script i is a calligraphic form of lowercase i. In a formula, its style distinguishes it from plain i and other styled letters. The Unicode 18.0 standard does not assign it one fixed mathematical value; the writer's equation supplies its meaning.

Unicode 18.0 notes that actual script glyphs vary across mathematical fonts, so the looped shape may differ even when the underlying character does not.

Why can 𝒾 turn into plain i?

NFKC and NFKD compatibility normalization can map it to plain i.

These Unicode cleanup forms fold mathematical alphabet characters to ordinary Latin or Greek letters, which can erase a distinction an equation relies on. NFC and NFD retain the script distinction.

Why is script i a separate character?

Its style can distinguish a variable from other i forms.

A Unicode proposal from 1999 describes script and bold-script alphabets as established mathematical styles and argues for storing each style as a separate character. That lets plain-text formulas preserve distinctions that styling alone could lose. Which quantity 𝒾 names still comes from the writer's notation.