(VAR x y z) (RULES .(1,x) -> x .(x,1) -> x .(i(x),x) -> 1 .(x,i(x)) -> 1 i(1) -> 1 i(i(x)) -> x .(i(y),.(y,z)) -> z .(y,.(i(y),z)) -> z .(.(x,y),z) -> .(x,.(y,z)) i(.(x,y)) -> .(i(y),i(x)) ) (COMMENT Example 17 in \cite{D33})