Using operators allows us to write very readable programs. Example: symbolic differentiation.
d( X, X, 1 ). d( U+V, X, A+B ) :- d( U, X, A ), d( V, X, B ). d( U*V, X, B*U+A*V ) :- d( U, X, A ), d( V, X, B ).
Read the second clause as
The differential of U+V with respect
to X is A+B if
the differential of U with respect
to X is A,
and the differential of V with
respect to X is B.
How much nicer this is than coding the structures in C or Pascal!