YES proof: The input problem is infeasible because [1] the following set of Horn clauses is satisfiable: c = c f(x, b) = b ==> g(x, a) = d f(x, a) = a ==> g(a, x) = c f(b, x) = b f(a, x) = a f(a, b) = b & f(a, a) = a ==> true__ = false__ true__ = false__ ==> \bottom This holds because [2] the following E does not entail the following G (Claessen-Smallbone's transformation (2018)): E: f(a, x) = a f(b, x) = b t1(b, x) = d t1(f(x, b), x) = g(x, a) t2(a, x) = c t2(f(x, a), x) = g(a, x) t3(b, a) = false__ t3(f(a, b), f(a, a)) = true__ t4(false__) = true__ t4(true__) = false__ G: true__ = false__ This holds because [3] the following ground-complete ordered TRS entails E but does not entail G: c -> t1(a, a) f(a, x) -> a f(b, x) -> b g(a, x) -> t2(f(x, a), x) g(x, a) -> t1(f(x, b), x) t1(b, x) -> d t2(a, x) -> t1(a, a) t3(a, a) -> true__ t3(b, a) -> false__ t4(false__) -> true__ t4(true__) -> false__ with the LPO induced by t3 > g > t2 > c > t1 > a > b > d > t4 > f > false__ > true__