YES exiting with thread! (VAR x y z ) (RULES f(f(x,y),z) -> f(x,f(y,z)) f(x,i(x)) -> e f(x,e) -> x f(e,x) -> x i(f(y,x)) -> f(i(x),i(y)) i(e) -> e f(x,f(i(x),z)) -> z i(i(x)) -> x f(i(x),x) -> e f(i(x),f(x,z)) -> z )