YES Problem: h(x) -> g(x) g(x) -> h(x) f(x,y) -> f(y,x) f(g(x),h(y)) -> f(x,y) f(h(x),h(y)) -> f(y,x) Proof: AT confluence processor Complete TRS T' of input TRS: f(g(x),h(y)) -> f(x,y) f(h(x),h(y)) -> f(y,x) f(g(x),g(y)) -> f(y,x) f(h(y),g(x)) -> f(y,x) h(x) -> g(x) g(x) -> h(x) f(x,y) -> f(y,x) T' = (P union S) with TRS P:h(x) -> g(x) g(x) -> h(x) f(x,y) -> f(y,x) TRS S:f(g(x),h(y)) -> f(x,y) f(h(x),h(y)) -> f(y,x) f(g(x),g(y)) -> f(y,x) f(h(y),g(x)) -> f(y,x) S is linear and P is reversible. CP(S,S) = CP(S,P union P^-1) = f(x482,x483) = f(h(x483),g(x482)), f(x484,x485) = f(h(x485),g(x484)), f(x487,x486) = f(h(x487),h(x486)), f(x489,x488) = f(h(x489),h(x488)), f(x491,x490) = f(g(x491),g(x490)), f(x493,x492) = f(g(x493),g(x492)), f(x494,x495) = f(g(x495),h(x494)), f(x496,x497) = f(g(x497),h(x496)) CP(P union P^-1,S) = f(g(x),g(y)) = f(x,y), f(g(x),h(y)) = f(y,x), f(h(x),g(y)) = f(y,x), f(g(y),g(x)) = f(y,x), f(h(x),h(y)) = f(x,y), f(h(y),h(x)) = f(y,x), f(h(y),g(x)) = f(x,y) We have to check termination of S: Matrix Interpretation Processor: dim=1 interpretation: [g](x0) = 6x0 + 4, [h](x0) = 7x0, [f](x0, x1) = x0 + 4x1 orientation: f(g(x),h(y)) = 6x + 28y + 4 >= x + 4y = f(x,y) f(h(x),h(y)) = 7x + 28y >= 4x + y = f(y,x) f(g(x),g(y)) = 6x + 24y + 20 >= 4x + y = f(y,x) f(h(y),g(x)) = 24x + 7y + 16 >= 4x + y = f(y,x) problem: f(h(x),h(y)) -> f(y,x) Matrix Interpretation Processor: dim=1 interpretation: [h](x0) = 3x0 + 1, [f](x0, x1) = 2x0 + x1 orientation: f(h(x),h(y)) = 6x + 3y + 3 >= x + 2y = f(y,x) problem: Qed