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A triangle on its side, marking a subgroup closed under conjugation.
Also known as: Is a normal subgroup of, Normality sign, Triangle subgroup sign
A sideways triangle marks a normal subgroup: one that stays put when the group acts on it by conjugation. Normality is what allows a quotient group to be formed, which is why the notation is given its own character rather than being written out.
States that the left group is a normal subgroup of the right one, invariant under conjugation by every element.
Contexts: Mathematics
Is the condition allowing a quotient group to be formed, which is why algebra texts mark it rather than describing it each time.
Contexts: Mathematics
A solid triangle lying on its side with its point facing right, sometimes ruled underneath with a short horizontal line.