Thread: Least Upper Bound proof

Any help with this proof would be appreciated:

If x1 and x2 are least upper bounds for A, then x1 = x2

least upper bound of A is denoted by sup(A)

Thanks!

The least upper bound means "less than or equal to any upper bound." Thus, x1 <= x2 and x2 <= x1. Also, <= is antisymmetric.