Back Blackboard bold Afrikaans Negreta de pissarra Catalan Buchstabe mit Doppelstrich German Negrita de pizarra Spanish Arbeleko letra lodi Basque Gras de tableau noir French Grassetto da lavagna Italian 黒板太字 Japanese 칠판 볼드체 Korean Blackboard bold Portuguese

Blackboard bold

A blackboard displaying the definition: The set of complex numbers consists of all quantities a + bi such that a and b are elements of the real numbers, and i squared equals negative one. Symbolically,
Blackboard bold used on a blackboard

Blackboard bold is a style of writing bold symbols on a blackboard by doubling certain strokes, commonly used in mathematical lectures, and the derived style of typeface used in printed mathematical texts. The style is most commonly used to represent the number sets (natural numbers), (integers), (rational numbers), (real numbers), and (complex numbers).

To imitate a bold typeface on a typewriter, a character can be typed over itself (called double-striking);[1] symbols thus produced are called double-struck, and this name is sometimes adopted for blackboard bold symbols,[2] for instance in Unicode glyph names.

In typography, a typeface with characters that are not solid is called inline, handtooled, or open face.[3]

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