The relationship between two analytic expressions. Given two analytic expressions, if any number or array in the common part (or subset of the common part) of their domain (see function) has the same value, they are said to be the same. For example, x2-y2 and (x+y) (x-y), for.
Whether two analytic expressions are the same or not depends on the specified number set, because the same two analytic expressions are the same in one number set and may be different in the other. For example, for x, they are the same in the non-negative real number set, but different in the real number set.