% Query: log(g,f)
minus(X,0,X).
minus(s(X),s(Y),Z):- minus(X,Y,Z).
p(quot(0,s(Y)),0).
p(quot(s(X),s(Y)),s(Z)):- minus(X,Y,U), p(quot(U,s(Y)),Z).
log(s(0),0).
log(s(s(X)),s(Y)):- p(quot(X,s(s(0))),U), log(s(U),Y).