+fun lookupContext (_, _, cs) name = SS.member (cs, name)
+
+fun bindType (ts, vs, cs) name = (SS.add (ts, name), vs, cs)
+fun bindVal (ts, vs, cs) (name, t, eqo) = (ts, SM.insert (vs, name, (t, eqo)), cs)
+fun bindContext (ts, vs, cs) name = (ts, vs, SS.add (cs, name))