LOCAL WolfGoatCabbage.


% PREDICATE  Initial : State.

Initial(St({Farmer,Wolf,Goat,Cabbage}, {})).


% PREDICATE  Final : State.

Final(St({}, {Farmer,Wolf,Goat,Cabbage})).


% PREDICATE  Applicable : Move * State.

Applicable(LeftToRight({Farmer}), St(left,_)) <-
               Farmer In left.

Applicable(RightToLeft({Farmer}), St(_,right)) <-
               Farmer In right.

Applicable(LeftToRight({Farmer,x}), St(left,_)) <-
               {Farmer,x} Subset left &
               x In {Wolf,Goat,Cabbage}.

Applicable(RightToLeft({Farmer,x}), St(_,right)) <-
               {Farmer,x} Subset right &
               x In {Wolf,Goat,Cabbage}.


% PREDICATE  ApplyMove : Move * State * State.

ApplyMove(LeftToRight(cargo), St(left,right), St(left\cargo,right+cargo)).

ApplyMove(RightToLeft(cargo), St(left,right), St(left+cargo,right\cargo)).


% PREDICATE  Legal : State.

Legal(St(left,right)) <-
               ~ Illegal(left) &
               ~ Illegal(right).


PREDICATE Illegal : Set(Object).

Illegal(bank) <-
               ~ Farmer In bank &
               ({Goat,Cabbage} Subset bank \/ {Wolf,Goat} Subset bank).