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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 ...
Blackboard bold. The blackboard bold typeface is widely used for denoting the basic number systems. These systems are often also denoted by the corresponding uppercase bold letter. A clear advantage of blackboard bold is that these symbols cannot be confused with anything else.
For example, is a rational number, as is every integer (e.g., =). The set of all rational numbers, also referred to as " the rationals ", [2] the field of rationals [3] or the field of rational numbers is usually denoted by boldface Q , or blackboard bold Q . {\displaystyle \mathbb {Q} .}
The blackboard bold letter style originated in the 1960s to distinguish bold letters from ordinary letters on a blackboard or using a typewriter; in professionally typeset documents, bold fonts were used for the same purpose. Since then, blackboard bold has gradually gained currency, and is now commonly used in mathematical printing to denote ...
Sample of a blackboard bold font, as produced by LaTeX with the amssymb package, at high resolution. Date: 2 December 2006: Source: en:Image:Blackboard bold.png: Author: Bryan Derksen, conversion of public domain png created by en:User:Deco: Permission (Reusing this file)
Integer. An integer is the number zero ( 0 ), a positive natural number (1, 2, 3, etc.) or a negative integer ( −1, −2, −3, etc.). [1] The negative numbers are the additive inverses of the corresponding positive numbers. [2] The set of all integers is often denoted by the boldface Z or blackboard bold .
Uses. Reusable writing surface on which text or drawings are made. A blackboard or a chalkboard is a reusable writing surface on which text or drawings are made with sticks of calcium sulphate or calcium carbonate, known, when used for this purpose, as chalk. Blackboards were originally made of smooth, thin sheets of black or dark grey slate stone.
The set of real numbers, sometimes called "the reals", is traditionally denoted by a bold R, often using blackboard bold, . The adjective real, used in the 17th century by René Descartes, distinguishes real numbers from imaginary numbers such as the square roots of −1.