%Source: http://colin.barker.pagesperso-orange.fr/sands.htm %query:triangle(g,f). /* triangle(N,T) is true if T is the Nth triangular number. */ triangle(N,T):-triangle(N,0,T). triangle(0,A,A). triangle(N,A,T):-N>0, N1 is N - 1, B is A+N, triangle(N1,B,T).
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