求助人工智能农夫过河问题的prolog语言程序

/*
PROBLEM:
A farmer with his goat, wolf and cabbage come to a river that they
wish to cross. There is a boat, but it only has room for two, and
the farmer is the only one that can row. If the goat and cabbage
get in the boat at the same time, the cabbage gets eaten.
Similarly, if the wolf and goat are together without the farmer,
the goat is eaten. Devise a series of crossings of the river so that all
concerned make it across safely.
The state of the system is indicated by stating where the farmer, the goat
the wolf and the cabbage are located.
state( Farmer, Wolf, Goat, Cabbage )
The problem is that a state must only be visited once, and some states
are illegal. This is checked by 'unsafe' and 'member'.
The Predicate "go" can be called with a start state and a final state
go( state(east,east,east,east), state(west,west,west,west) ).
*/
DOMAINS
LOC = east ;