Operator definitions in Prolog look like this:

:- op(Precedence, Type, Name).
%Precedence is a number between 0 and 1200.
%Type is an atom specifying type and associativity of operator

There are the following possibilities for what Type may look like:

• infix xfx, xfy, yfx
• prefix fx, fy
• suffix xf, yf

  x stands for an argument with lower precedence than operator f
  y stands for an argument with lower or equal precedence than operator f