What ⅅ means
In some formulas, it marks the uppercase differential.
Unicode groups it with the lowercase differential ⅆ, exponential symbol ⅇ, and imaginary units ⅈ and ⅉ (both square roots of 1). Font designs vary in serifs and stroke placement; local convention may set these forms upright or italic.
Blackboard bold grew from doubled chalk strokes; similar typewriter tricks carried it into mathematical print by the mid-20th century.
Specialist math notation; follow the author's convention.
Don't equate it with upright double-struck 𝔻.
Part of the collection
Don't confuse it with
2
Questions people ask
1Why does ⅅ show as a box on some devices?
Because that device's fonts have no glyph for it. The character is still correct and still copies correctly — the box is a missing glyph, not a broken character.
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How to type or find ⅅ
- Search it as
- blackboard bold D · differential D · italic D
- Shows up in
- Anything that takes text · its shape is whatever your font draws
ⅅ\2145unicode-math, \mitBbbD selects this italic form; \mathbb{D} yields upright 𝔻.Codes and encoding1 code points
A visible symbol can contain several code points. JS .length counts UTF-16 units; UTF-8 counts bytes.