+increaseStrictSigArity :: Int -> StrictSig -> StrictSig
+-- Add extra arguments to a strictness signature
+increaseStrictSigArity arity_increase (StrictSig (DmdType env dmds res))
+ = StrictSig (DmdType env (replicate arity_increase topDmd ++ dmds) res)
+
+isTopSig :: StrictSig -> Bool