diff --git a/core-elm/Either.elm b/core-elm/Either.elm
index dd679dc..8b5bee3 100644
--- a/core-elm/Either.elm
+++ b/core-elm/Either.elm
@@ -1,12 +1,22 @@
 
 data Either a b = Left a | Right b
 
+either : (a -> c) -> (b -> c) -> Either a b -> c
 either f g e = case e of { Left x -> f x ; Right y -> g y }
 
+
+isLeft  : Either a b -> Bool
 isLeft  e = case e of { Left  _ -> True ; _ -> False }
+
+isRight : Either a b -> Bool
 isRight e = case e of { Right _ -> True ; _ -> False }
 
+
+lefts  : [Either a b] -> [a]
 lefts  = Elm.List.filter isLeft
+
+rights : [Either a b] -> [b]
 rights = Elm.List.filter isRight
 
+partition : [Either a b] -> ([a],[b])
 partition = Elm.List.partition isLeft
\ No newline at end of file