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Vertical bars around a set, counting its members.
Also known as: Set cardinality, Size of a set, Bars around a set
Bars around a set give its cardinality — its number of elements, finite or infinite. For infinite sets the notation is doing real work: |ℕ| and |ℝ| are both infinite and are not equal, which is Cantor's theorem in one line.
Denotes the cardinality of a set: how many elements it has.
Contexts: Mathematics
Distinguishes sizes of infinity: the integers and the reals both have infinitely many elements and different cardinalities.
Contexts: Mathematics
Shares its glyph with absolute value, group order and matrix determinant, distinguished only by what it encloses.
Contexts: Mathematics
Two upright parallel strokes of equal height enclosing a set name or a braced list.