/*
s([on(0,1)],P).
P = 0.166666666666667 ?;
s([\+ on(0,6)],P).
P = 0.833333333333333  ?;


s([on(1,1)],P).
P = 0.138888888888889 ?
s([on(1,6)],P).
P = 0.138888888888889 ?
s([on(2,1)],P).
out of memory
s([on(0,1),on(1,1)],P).
P = 0.0277777777777778 ?
s([on(0,1),on(1,1),on(2,1)],P).
P = 0.00462962962962963 ?




*/
on(0,1):1/6;on(0,2):1/6;on(0,3):1/6;
on(0,4):1/6;on(0,5):1/6;on(0,6):1/6.

on(X,1):1/6;on(X,2):1/6;on(X,3):1/6;
on(X,4):1/6;on(X,5):1/6;on(X,6):1/6:-
  X1 is X-1,X1>=0,on(X1,_),
  \+ on(X1,6).