To denote the fact that A is a superset of B we write A ⊇ B in this encyclopedia. (Some browsers may not be able to display this symbol, or the other superset and subset symbols used in this paragraph.) Many mathematicians write A ⊃ B instead, although others use this to mean that A is a proper superset of B (that is, A is a superset of B and not equal to it). A ⊇ B is equivalent to B ⊆ A, and A ⊃ B is equivalent to B ⊂ A.