10.35.13.3 Operator Declarations

     :- op(1200, xfx, [+:,-:,+?,-?]).
     :- op(760, yfx, #<=>).
     :- op(750, xfy, #=>).
     :- op(750, yfx, #<=).
     :- op(740, yfx, #\/).
     :- op(730, yfx, #\).
     :- op(720, yfx, #/\).
     :- op(710, fy, #\).
     :- op(700, xfx, [in,in_set]).
     :- op(700, xfx, [#=,#\=,#<,#=<,#>,#>=]).
     :- op(550, xfx, ..).
     :- op(500, fy, \).
     :- op(490, yfx, ?).
     :- op(400, yfx, [/>,/<]).