4hour_dom(D) :- D .>. 0, D .<. 23.
    5
    6switch :- not neg_switch.
    7neg_switch :- not switch.
    8
    9lightOn :- switch, not am.
   10
   11% :- not lightOn.
   12
   13am :- not neg_am.
   14neg_am :- not am.
   15
   16hour(X) :- hour_dom(X), X .>=. 12, not am.
   17hour(X) :- hour_dom(X), X .<. 12, am.
   18
   19light_is(on) :- lightOn.
   20light_is(off) :- not lightOn