Commutator and negator functions

You can specify a commutator function only for user-defined routines written in C.

The database server calls a commutator or a negator function instead of the original function if the query optimizer determines that it is faster. A commutator function returns the same Boolean result as the original function with the same arguments but with the arguments in reverse order. A negator returns the opposite Boolean result as the original function with the same arguments in the same order.