Set (mathematics)
Membership

If B is a set and x is an element of B, this is written in shorthand as x ∈ B, which can also be read as " x belongs to B ", or " x is in B ". The statement " y is not an element of B " is written as y ∉ B, which can also be read as " y is not in B ".

For example, with respect to the sets A = {1, 2, 3, 4}, B = {blue, white, red}, and F = { n | n is an integer, and 0 ≤ n ≤ 19},
punctuation:no_comma