YES proof: The input problem is infeasible because [1] the following set of Horn clauses is satisfiable: div(s(x), s(y)) = pair(s(q), r) div(s(x), s(y)) = pair(0, s(x)) div(0, s(x)) = pair(0, 0) m(s(x), s(y)) = m(x, y) m(x, 0) = x m(0, s(y)) = 0 lt(s(x), s(y)) = lt(x, y) lt(0, s(x)) = true lt(x, 0) = false lt(x1, x2) = true & lt(x1, x2) = false & div(m(x1, x2), s(x2)) = pair(x3, x4) ==> true__ = false__ true__ = false__ ==> \bottom This holds because [2] the following E does not entail the following G (Claessen-Smallbone's transformation (2018)): E: div(0, s(x)) = pair(0, 0) div(s(x), s(y)) = pair(0, s(x)) div(s(x), s(y)) = pair(s(q), r) lt(0, s(x)) = true lt(s(x), s(y)) = lt(x, y) lt(x, 0) = false m(0, s(y)) = 0 m(s(x), s(y)) = m(x, y) m(x, 0) = x t1(lt(x1, x2), lt(x1, x2), div(m(x1, x2), s(x2)), x3, x4) = true__ t1(true, false, pair(x3, x4), x3, x4) = false__ t2(false__) = true__ t2(true__) = false__ G: true__ = false__ This holds because [3] the following ground-complete ordered TRS entails E but does not entail G: pair(0, s(X0)) = pair(0, s(X1)) pair(0, s(X0)) = pair(s(X1), X2) pair(s(X0), X1) = pair(s(X2), X3) div(0, s(X0)) -> pair(0, 0) div(s(X0), s(X1)) -> pair(0, s(X0)) lt(0, s(X0)) -> true lt(X0, 0) -> false lt(s(X0), s(X1)) -> lt(X0, X1) m(0, s(X0)) -> 0 m(X0, 0) -> X0 m(s(X0), s(X1)) -> m(X0, X1) t1(X0, X0, Z1, X2, X3) -> true__ t1(X0, X0, div(Z1, s(X2)), X3, X4) -> true__ t1(X0, X0, div(Z1, s(s(X2))), X3, X4) -> true__ t1(X0, X0, pair(0, 0), X1, X2) -> true__ t1(true, false, Z1, 0, s(X2)) -> false__ t1(true, false, Z1, X0, X1) -> false__ t1(true, false, Z1, s(X1), X2) -> false__ t2(false__) -> true__ t2(true__) -> false__ with the LPO induced by t1 > div > pair > 0 > true > s > false > lt > m > t2 > false__ > true__