MAYBE Proof: ConCon could not decide confluence of the system. \cite{ALS94}, Theorem 4.1 does not apply. ConCon could not decide whether all critical pairs are joinable or not. cons(x, cons(x', z')) = cons($1, z') <= orient($1, $1) = pair(x, x'): For all conditions c 'tcap(c.lhs)' is unifiable with c.rhs.