diff --git a/expressions.cabal b/expressions.cabal
--- a/expressions.cabal
+++ b/expressions.cabal
@@ -1,6 +1,6 @@
 name:                expressions
-version:             0.1.1
-synopsis:            Expressions and Formulas a la carte
+version:             0.1.2
+synopsis:            Expressions and Formulae a la carte
 description:
   This package is aimed at providing means of fixing a first-order language and
   declaring sorted expressions and formulae, the types ensure the declared
@@ -70,12 +70,12 @@
                        TypeSynonymInstances,
                        UndecidableInstances
   build-depends:       attoparsec >=0.13 && <0.14,
-                       base >=4.9 && <4.10,
-                       containers >=0.5.7 && <0.5.8,
+                       base >=4.9 && <4.11,
+                       containers >=0.5.7 && <0.5.11,
                        lattices >=1.6 && <1.7,
-                       singletons >=2.2 && <2.3,
+                       singletons >=2.2 && <2.4,
                        text >=1.2 && <1.3,
-                       transformers >=0.5.2 && <0.5.3
+                       transformers >=0.5.2 && <0.5.5
   hs-source-dirs:      src
   default-language:    Haskell2010
   ghc-options:         -Wall
diff --git a/src/Data/Expression.hs b/src/Data/Expression.hs
--- a/src/Data/Expression.hs
+++ b/src/Data/Expression.hs
@@ -125,7 +125,7 @@
 import Control.Monad.Trans.Reader
 import Control.Monad.Trans.State
 import Data.List hiding (and, or, union)
-import Data.Map hiding (map, foldr, mapMaybe, partition)
+import Data.Map hiding (map, drop, foldr, mapMaybe, partition)
 import Data.Maybe
 import Data.Monoid
 import Data.Singletons