switch(1..3).
action(tog(X)) :- switch(X).

#program dynamic.
% Effect axioms
  c(sw(X),up)   :- 'h(sw(X),down), o(tog(X)).
  c(sw(X),down) :- 'h(sw(X),up), o(tog(X)).
  c(light,off)  :- 'h(light,on), o(tog(_)).
  c(light,on)   :- 'h(light,off), o(tog(_)).
% Executability constraints: none in this case
% Anything caused, also holds
  h(F,V) :- c(F,V).
  c(F) :- c(F,V).
% Inertia
  h(F,V) :- 'h(F,V), not c(F).

% Action generation
  1 { o(A): _action(A) } 1.