TYPE
 SE = Atom | Exp;
 Exp = L: SE-seq;
 Atom = A: INT;
ENDTYPE

par(e) = if (is-Atom(e) -> 0,
             is-Exp(e) -> 2 .+ add-red(0,par-seq(L(e))));


rev(e) = if (is-Atom(e) -> e,
             is-Exp(e) ->  (reverse _o_ rev-seq) (L(e)) );