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A circle crossed by a diagonal stroke, denoting the set with no members.
Also known as: Null set, Zero with a line through it, Circle with a slash
∅ denotes the empty set. André Weil introduced it in 1939 for the Bourbaki group, taking it from the Norwegian and Danish letter Ø — which is why the mathematical symbol is a circle with a straight slash rather than a zero.
Is encoded as U+2205 EMPTY SET, a character distinct from the Scandinavian letter Ø and from the slashed digit zero used in some typefaces.
Contexts: Mathematics
Denotes the unique set containing no members, which is a subset of every set.
Contexts: Mathematics
Was introduced by André Weil in 1939 for the Bourbaki group, adapted from the Norwegian and Danish letter Ø rather than from a struck-through zero.
Contexts: Mathematics
A single closed circle or narrow oval crossed by one straight diagonal stroke running from lower left to upper right and projecting slightly beyond it.
Near-identical characters from unrelated fields, substituted for each other constantly.
The empty set is a subset of every set, which is the first fact stated about it.