Hard matching example
				Diff(wa,nt)  Diff(wa,sa)  Diff(nt,q)  Diff(nt,sa)  Diff(q,nsw)  Diff(q,sa)  Diff(nsw,v)  Diff(nsw,sa)  Diff(v,sa)  Colorable() Diff(Red,Blue)      Diff (Red,Green) Diff(Green,Red)  Diff(Green,Blue) Diff(Blue,Red)      Diff(Blue,Green)
	l Colorable() is inferred iff the CSP has a solution l CSPs include 3SAT as a special case, hence matching is NP-hard