A teacher is on playground duty encounters a problem with a bully, a hungry nerd and an apple and he must escort these three to the office. The teacher, by school rules, can only escort one at a time to the office. This is compounded by the fact that if the bully is left with the nerd the bully will beat up the nerd and if the nerd is left with the apple then the nerd will eat the apple. This will happen both in the playground as well as in the office.

move(state(X,X,X,notsolved),
  solved,
  state(X,X,X,solved)).
move(state(P1,B,A,notsolved),
  movenerd(P1,P2),
  state(P2,B,A,notsolved)).
move(state(N, P1, P,notsolved),
  moveapple(P1,P2),
  state(N, P2, B,notsolved)).
move(state(N, A, P1,notsolved),
  movebully(P1, P2),
  state(N, A, P2, H,notsolved)).
escort(state(_,_,_,solved)).
  escort(OldState) :-
  move(OldState, Move, NewState),
  escort(NewState),
  write(Newstate),
  nl.