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A struck-through epsilon, denying membership of a set.
Also known as: Not in, Is not a member of, Not element of
The not-an-element sign denies membership: the thing on the left is not in the set on the right. It is the ordinary negation stroke applied to the membership sign, and the same stroke negates most relations in mathematics, so recognising the convention is worth more than memorising the character.
Denies set membership: the object named on the left is not one of the elements of the set named on the right.
Contexts: Mathematics
Follows the general convention that a diagonal stroke through a relation sign negates it, which also gives the not-equal, not-subset and does-not-divide signs.
Contexts: Mathematics
A rounded letter e with a horizontal middle bar, crossed by a diagonal stroke running from lower left to upper right.
The negation of set membership.