%Source: http://colin.barker.pagesperso-orange.fr/sands.htm
%query:between(g,g,f).
/* between(I,J,K) is true if K is an integer between I and J inclusive.    */
between(I,J,J):-J>=I.
between(I,J,K):-J>I, J1 is J - 1, between(I,J1,K).