+-- pprTrace "makeTrivial" (vcat [ppr var <+> ppr (exprArity (substExpr env' (Var var)))
+-- , ppr expr
+-- , ppr (substExpr env' (Var var))
+-- , ppr (idArity (fromJust (lookupInScope (seInScope env') var))) ]) $
+ ; return (env', substExpr env' (Var var)) }
+ -- The substitution is needed becase we're constructing a new binding
+ -- a = rhs
+ -- And if rhs is of form (rhs1 |> co), then we might get
+ -- a1 = rhs1
+ -- a = a1 |> co
+ -- and now a's RHS is trivial and can be substituted out, and that
+ -- is what completeNonRecX will do