% a simplification of the preference
% between taxi and other actions 
% does not want to take taxi to school 

desire(L):- literal(L).

desire(cost1).
isor(cost1, taxiAvl(home), taxiAvl(school)).

desire(cost2).
isor(cost2, cost1, taxiAvl(station)).

desire(cost3).
isnegation(cost3, cost2).

desire(cost).
always(cost, cost3).

maximize {satisfy(cost,0)}.