import planner.

main =>
    S0=[s,s,s,s],
%    best_plan(S0,Plan),
    plan_unbounded(S0,Plan),
%    best_plan_unbounded(S0,Plan),
    writeln(Plan).

final([n,n,n,n]) => true.

action([F,F,G,C],S1,Action,ActionCost) ?=>
    Action=farmer_wolf,
    ActionCost=1,
    opposite(F,F1),
    S1=[F1,F1,G,C],
    not unsafe(S1).
action([F,W,F,C],S1,Action,ActionCost) ?=>
    Action=farmer_goat,
    ActionCost=1,
    opposite(F,F1),
    S1=[F1,W,F1,C],
    not unsafe(S1).
action([F,W,G,F],S1,Action,ActionCost) ?=>
    Action=farmer_cabbage,
    ActionCost=1,
    opposite(F,F1),
    S1=[F1,W,G,F1],
    not unsafe(S1).
action([F,W,G,C],S1,Action,ActionCost) =>
    Action=farmer_alone,
    ActionCost=1,
    opposite(F,F1),
    S1=[F1,W,G,C],
    not unsafe(S1).

index (+,-) (-,+)
opposite(n,s).
opposite(s,n).

unsafe([F,W,G,_C]),W==G,F!==W => true.
unsafe([F,_W,G,C]),G==C,F!==G => true.