%Source: http://colin.barker.pagesperso-orange.fr/sands.htm
%query:power(g,g,f).
/* power(X,N,V) is true if V is X to the Nth power.                       */
power(0,N,0):-N>0.
power(X,0,1):-X>0.
power(X,N,V):-X>0, N>0, N1 is N - 1, power(X,N1,V1), V is V1*X.