Def z@x == z @ x

Thm* A:Type, R:(A*A*Prop). (EquivRel x,y:A*. x R y) (x,y,z:A*. (x R y) ((z @ x) R (z @ y))) (z:A*, y:x,y:A*//(x R y). z@y x,y:A*//(x R y))

Def as @ bs == Case of as; nil bs ; a.as' a.(as' @ bs) (recursive)

Thm* T:Type, as,bs:T*. (as @ bs) T*