2A pair (X,∘), where ∘ is a binary operation on X, is a group if ∘ is associative, X has an identity element, and every
x 
X has an inverse.
2A pair (X,∘), where ∘ is a binary operation on X, is a group if ∘ is associative, X has an identity element, and every
x X has an inverse.