#const w=12.
#const n = 2*w+1.
#const q = 4*w.

wheel(1..w).
inner(0;1).

edge(Y*w+X,n) :- wheel(X), inner(Y).
edge(Y*w+X,Y*w+X+1) :- wheel(X), wheel(X+1), inner(Y).
edge(Y*w+w,Y*w+1) :- inner(Y).
