domains
X1, X2, Y1, Y2 = REAL
N = INTEGER
predicates
serp(X1,X2,Y1,Y2,N)
clauses
serp:-
XN1=2*X1/3+X2/3,
XN2 := X1/3 + 2*X2/3,
YN1 := 2*Y1/3 + Y2 / 3,
YN2 := Y1/3+2*Y2/3,
rectangle(round(XN1,round(YN1),round(XN2),round(YN2))),
serp(X1, Y1, XN1, YN1, N-1),
serp(XN1, Y1, XN2, YN1, N-1),
serp(XN2, Y1, X2, YN1, N-1),
serp(X1, YN1, XN1, YN2, N-1),
serp(XN2, YN1, X2, YN2, N-1),
serp(X1, YN2, XN1, Y2, N-1),
serp(XN1, YN2, XN2, Y2, N-1),
serp(XN2, YN2, X2, Y2, N-1).

goal
initgraph(1,0,"c:\\prolog"), setcolor(2),
serp(20, 20, 460, 460, 4).