(VAR x y z u v) (RULES f(f(x,y,z),u,f(x,y,v)) -> f(x,y,f(z,u,v)) f(x,y,y) -> y f(x,y,g(y)) -> x f(x,x,y) -> x f(g(x),x,y) -> y ) (COMMENT Example 4.48 (Ternary Boolean Algebra) in \cite{SK90})