12.4.18.1 Term Comparison

int PL_compare(term_t t1, term_t t2)

Compares two terms using the standard order of terms and returns -1, 0 or 1. See also compare/3. If the terms are cyclic terms that have no order (see section 4.6.1) and the Prolog flag incomparable is error, it raises an exception and returns -2. -2 is also returned if the comparison raises a resource error. Code that tests the result using < 0 must first test for -2.

bool PL_same_compound(term_t t1, term_t t2)

Yields TRUE if t1 and t2 refer to physically the same compound term and FALSE otherwise.