diff --git a/lib/Haskell/Data/Map.agda b/lib/Haskell/Data/Map.agda
new file mode 100644
index 00000000..f5a4e6cd
--- /dev/null
+++ b/lib/Haskell/Data/Map.agda
@@ -0,0 +1,199 @@
+-- An incomplete interface of
+-- Haskell's Data.Map.
+-- See https://hackage.haskell.org/package/containers-0.4.0.0/docs/src/Data-Map.html.
+
+-- We don't actually implement maps;
+-- we only postulate an interface
+-- and some basic properties.
+
+module Haskell.Data.Map where
+
+open import Agda.Builtin.Unit
+open import Agda.Builtin.Bool
+open import Agda.Builtin.Nat hiding (_<_)
+open import Agda.Builtin.Int
+open import Agda.Builtin.List
+open import Haskell.Prim.Bool
+open import Haskell.Prim.Maybe
+open import Haskell.Prim.Monoid
+open import Haskell.Prim.Ord
+open import Haskell.Prim.Tuple
+import Haskell.Prim.String
+open import Haskell.Prim using (case_of_; _$_; _≡_; if_then_else_; ⊥; IsTrue; IsFalse)
+open import Haskell.Prelude using (error)
+
+variable
+  k v a b : Set
+
+postulate
+  Map : (k a :  Set) -> Set
+
+  iMonoidMap : {k v : Set} {{ordk : Ord k}} -> Monoid (Map k v)
+
+  -- Constructs an empty map.
+  empty : Map k a
+
+  -- | /O(1)/. Is the map empty?
+  --
+  -- > Data.Map.null (empty)           == True
+  -- > Data.Map.null (singleton 1 'a') == False
+  null : Map k a -> Bool
+  @0 emptyIsNull : ∀ {k a : Set} -> IsTrue (null (empty {k} {a}))
+
+  -- | /O(1)/. The number of elements in the map.
+  --
+  -- > size empty                                   == 0
+  -- > size (singleton 1 'a')                       == 1
+  -- > size (fromList([(1,'a'), (2,'c'), (3,'b')])) == 3
+  size : Map k a -> Nat   -- should we use Nat or Int here?
+  @0 nullHasSize0 : ∀ (map : Map k a) -> IsTrue (null map) -> size map ≡ 0
+
+  -- | /O(log n)/. Lookup the value at a key in the map.
+  --
+  -- The function will return the corresponding value as @('Just' value)@,
+  -- or 'Nothing' if the key isn't in the map.
+  lookup : {{ordk : Ord k}} -> k -> Map k a -> Maybe a
+
+  -- Same, but returns a tuple with the key and the value.
+  lookupAssoc : {{ordk : Ord k}} -> Map k a -> Maybe (k × a)
+
+  -- | /O(log n)/. Is the key a member of the map? See also 'notMember'.
+  --
+  -- > member 5 (fromList [(5,'a'), (3,'b')]) == True
+  -- > member 1 (fromList [(5,'a'), (3,'b')]) == False
+  member : {{ordk : Ord k}} -> k -> Map k a -> Bool
+
+notMember : {{ordk : Ord k}} -> k -> Map k a -> Bool
+notMember key map = not (member key map)
+
+postulate
+  @0 notMember↔Nothing : {{ordk : Ord k}} -> ∀ (key : k) (map : Map k a)
+                            -> IsFalse (member key map) ↔ lookup key map ≡ Nothing
+  @0 nullHasNoMembers : {{ordk : Ord k}} -> ∀ (map : Map k a) -> IsTrue (null map)
+                          -> ∀ (key : k) -> IsFalse (member key map)
+
+  -- | /O(log n)/. Find the value at a key.
+  -- Calls 'error' when the element can not be found.
+  -- Consider using 'lookup' when elements may not be present.
+  find : {{ordk : Ord k}} (key : k) (map : Map k a) -> @0 IsTrue (member key map)
+           -> a
+  @0 findSameAsLookup : {{ordk : Ord k}} (key : k) (map : Map k a) (@0 isMember : IsTrue (member key map))
+                          -> lookup key map ≡ Just (find key map isMember)
+
+-- I think it's easier to write a definition here.
+findWithDefault : {{ordk : Ord k}} -> a -> k -> Map k a -> a
+findWithDefault def k m = case lookup k m of λ where
+    Nothing   -> def
+    (Just x)  -> x
+
+postulate
+  singleton : k -> a -> Map k a
+  @0 singletonHasItsElement : {{ordk : Ord k}} -> ∀ (key : k) (val : a)
+                                -> lookup key (singleton key val) ≡ Just val
+  
+  {--------------------------------------------------------------------
+    Insertion
+  --------------------------------------------------------------------}
+  -- | /O(log n)/. Insert a new key and value in the map.
+  -- If the key is already present in the map, the associated value is
+  -- replaced with the supplied value. 'insert' is equivalent to
+  -- @'insertWith' 'const'@.
+  --
+  -- > insert 5 'x' (fromList [(5,'a'), (3,'b')]) == fromList [(3, 'b'), (5, 'x')]
+  -- > insert 7 'x' (fromList [(5,'a'), (3,'b')]) == fromList [(3, 'b'), (5, 'a'), (7, 'x')]
+  -- > insert 5 'x' empty                         == singleton 5 'x'
+  insert : {{ordk : Ord k}} -> k -> a -> Map k a -> Map k a
+  @0 memberAfterInsertion : {{ordk : Ord k}} -> ∀ (key : k) (val : a) (map : Map k a)
+                              -> lookup key (insert key val map) ≡ Just val
+  @0 sizeIncreasesAfterInsertion : {{ordk : Ord k}}  -> ∀ (key : k) (val : a) (map : Map k a)
+                              -> @0 IsFalse (member key map)
+                              -> size (insert key val map) ≡ suc (size map)
+  @0 sizeRemainsAfterInsertion : {{ordk : Ord k}}  -> ∀ (key : k) (val : a) (map : Map k a)
+                              -> @0 IsTrue (member key map)
+                              -> size (insert key val map) ≡ size map
+
+-- | /O(n*log n)/. Build a map from a list of key\/value pairs. See also 'fromAscList'.
+-- If the list contains more than one value for the same key, the last value
+-- for the key is retained.
+fromList : {{ordk : Ord k}} -> List (k × a) -> Map k a
+fromList [] = empty
+fromList ((key , val) ∷ xs) = insert key val (fromList xs)
+
+postulate
+  -- | /O(log n)/. Insert with a function, combining key, new value and old value.
+  -- @'insertWithKey' f key value mp@ 
+  -- will insert the pair (key, value) into @mp@ if key does
+  -- not exist in the map. If the key does exist, the function will
+  -- insert the pair @(key,f key new_value old_value)@.
+  -- Note that the key passed to f is the same key passed to 'insertWithKey'.
+  --
+  -- > let f key new_value old_value = (show key) ++ ":" ++ new_value ++ "|" ++ old_value
+  -- > insertWithKey f 5 "xxx" (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "5:xxx|a")]
+  -- > insertWithKey f 7 "xxx" (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "a"), (7, "xxx")]
+  -- > insertWithKey f 5 "xxx" empty                         == singleton 5 "xxx"
+
+  insertWithKey : {{ordk : Ord k}} -> (k -> a -> a -> a) -> k -> a -> Map k a -> Map k a
+  @0 insertWithKeyIfMember : {{ordk : Ord k}}
+                            -> ∀ (f : k -> a -> a -> a) (key : k) (newval : a) (map : Map k a)
+                            -> (@0 isMember : IsTrue (member key map))
+                            -> insertWithKey f key newval map ≡ insert
+                                                                  key
+                                                                  (f key newval (find key map isMember))
+                                                                  map
+  @0 insertWithKeyIfNotMember : {{ordk : Ord k}}
+                            -> ∀ (f : k -> a -> a -> a) (key : k) (newval : a) (map : Map k a)
+                            -> (@0 isNotMember : IsFalse (member key map))
+                            -> insertWithKey f key newval map ≡ insert key newval map
+
+-- | /O(log n)/. Insert with a function, combining new value and old value.
+-- @'insertWith' f key value mp@ 
+-- will insert the pair (key, value) into @mp@ if key does
+-- not exist in the map. If the key does exist, the function will
+-- insert the pair @(key, f new_value old_value)@.
+insertWith : {{ordk : Ord k}} -> (a -> a -> a) -> k -> a -> Map k a -> Map k a
+insertWith f key newval map = insertWithKey (λ _ new old -> f new old) key newval map
+
+-- | /O(log n)/. Combines insert operation with old value retrieval.
+-- The expression (@'insertLookupWithKey' f k x map@)
+-- is a pair where the first element is equal to (@'lookup' k map@)
+-- and the second element equal to (@'insertWithKey' f k x map@).
+insertLookupWithKey : {{ordk : Ord k}} -> (k -> a -> a -> a) -> k -> a -> Map k a
+                   -> (Maybe a × Map k a)
+insertLookupWithKey f key newval map = lookup key map , insertWithKey f key newval map
+
+postulate
+  {--------------------------------------------------------------------
+    Deletion
+    [delete] is the inlined version of [deleteWith (\k x -> Nothing)]
+  --------------------------------------------------------------------}
+  -- | /O(log n)/. Delete a key and its value from the map. When the key is not
+  -- a member of the map, the original map is returned.
+  delete : {{ordk : Ord k}} -> k -> Map k a -> Map k a
+  @0 notMemberAfterDeletion : {{ordk : Ord k}} -> ∀ (key : k) (map : Map k a)
+                                -> IsFalse (member key (delete key map))
+  @0 sizeDecreasesAfterDeletion : {{ordk : Ord k}} -> ∀ (key : k) (map : Map k a)
+                                -> @0 IsTrue (member key map)
+                                -> size map ≡ suc (size (delete key map))
+  {- This follows from the next one.
+  @0 sizeRemainsAfterDeletion : {{ordk : Ord k}} -> ∀ (key : k) (map : Map k a)
+                                -> @0 IsFalse (member key map)
+                                -> size map ≡ size (delete key map)
+  -}
+  @0 deletingWhatThereIsNot : {{ordk : Ord k}} -> ∀ (key : k) (map : Map k a)
+                                -> @0 IsFalse (member key map)
+                                -> map ≡ delete key map
+
+  @0 insertAndDelete : {{ordk : Ord k}} -> ∀ (key : k) (val : a) (map : Map k a)
+                                -> @0 IsFalse (member key map)
+                                -> delete key (insert key val map) ≡ map
+  @0 deleteAndInsert : {{ordk : Ord k}} -> ∀ (key : k) (map : Map k a)
+                                -> (@0 isMember : IsTrue (member key map))
+                                -> insert key (find key map isMember) (delete key map)
+                                     ≡ map
+
+  @0 insertNotChangingOthers : {{ordk : Ord k}} -> ∀ (key1 key2 : k) (val : a) (map : Map k a)
+                                -> lookup key1 (insert key2 val map) ≡ lookup key1 map
+  @0 deleteNotChangingOthers : {{ordk : Ord k}} -> ∀ (key1 key2 : k) (map : Map k a)
+                                -> lookup key1 (delete key2 map) ≡ lookup key1 map
+
+-- Done until delete.
diff --git a/lib/Haskell/Prim.agda b/lib/Haskell/Prim.agda
index 65f6e3f5..8aae64db 100644
--- a/lib/Haskell/Prim.agda
+++ b/lib/Haskell/Prim.agda
@@ -99,7 +99,7 @@ data ⊥ : Set where
 magic : {A : Set} → ⊥ → A
 magic ()
 
---principle of explosion
+-- principle of explosion
 exFalso : {x : Bool} → (x ≡ True) → (x ≡ False) → ⊥
 exFalso {False} () b 
 exFalso {True} a ()
diff --git a/lib/Haskell/Prim/Tuple.agda b/lib/Haskell/Prim/Tuple.agda
index f566e13b..fb4bf730 100644
--- a/lib/Haskell/Prim/Tuple.agda
+++ b/lib/Haskell/Prim/Tuple.agda
@@ -7,7 +7,7 @@ open import Haskell.Prim
 -- Tuples
 
 infix 3 _×_ _×_×_
-
+infix 2 _↔_
 infix -1 _,_ _,_,_
 
 record _×_ (a b : Set) : Set where
@@ -43,3 +43,7 @@ snd₃ (_ , y , _) = y
 
 thd₃ : (a × b × c) → c
 thd₃ (_ , _ , z) = z
+
+-- logical equivalence for proofs
+_↔_ : (A : Set) (B : Set) -> Set
+A ↔ B = (A → B) × (B → A)
diff --git a/test/AllTests.agda b/test/AllTests.agda
index 850f59bb..77b2a664 100644
--- a/test/AllTests.agda
+++ b/test/AllTests.agda
@@ -75,6 +75,9 @@ import Issue286
 import NonClassInstance
 import Issue218
 import Issue251
+import HaskellDataOpenImport
+import HaskellDataQualifiedImport
+import Map
 
 {-# FOREIGN AGDA2HS
 import Issue14
@@ -149,4 +152,7 @@ import Issue286
 import NonClassInstance
 import Issue218
 import Issue251
+import HaskellDataOpenImport
+import HaskellDataQualifiedImport
+import Map
 #-}
diff --git a/test/HaskellDataOpenImport.agda b/test/HaskellDataOpenImport.agda
new file mode 100644
index 00000000..e1a4467f
--- /dev/null
+++ b/test/HaskellDataOpenImport.agda
@@ -0,0 +1,10 @@
+{-# OPTIONS --erasure #-}
+
+module HaskellDataOpenImport where
+
+open import Agda.Builtin.Int
+open import Haskell.Data.Map
+
+map : Map Int Int
+map = empty
+{-# COMPILE AGDA2HS map #-}
diff --git a/test/HaskellDataQualifiedImport.agda b/test/HaskellDataQualifiedImport.agda
new file mode 100644
index 00000000..6cb0a5da
--- /dev/null
+++ b/test/HaskellDataQualifiedImport.agda
@@ -0,0 +1,10 @@
+{-# OPTIONS --erasure #-}
+
+module HaskellDataQualifiedImport where
+
+open import Agda.Builtin.Int
+import Haskell.Data.Map as Map
+
+map : Map.Map Int Int
+map = Map.empty
+{-# COMPILE AGDA2HS map #-}
diff --git a/test/Map.agda b/test/Map.agda
new file mode 100644
index 00000000..47248f5f
--- /dev/null
+++ b/test/Map.agda
@@ -0,0 +1,56 @@
+-- A test pack for Data.Map.
+module Map where
+
+open import Agda.Builtin.Equality
+open import Agda.Builtin.Nat
+open import Agda.Builtin.List
+open import Haskell.Prim.Maybe
+open import Haskell.Prim.Ord
+open import Haskell.Prim.Tuple
+open import Haskell.Law.Equality
+import Haskell.Data.Map as Map
+open Map using (Map)
+
+firstMap : Map Nat Nat
+firstMap = Map.fromList ((50 , 5) ∷ (40 , 4) ∷ (100 , 10) ∷ [])
+{-# COMPILE AGDA2HS firstMap #-}
+
+val1 : Maybe Nat
+val1 = Map.lookup 100 firstMap
+{-# COMPILE AGDA2HS val1 #-}
+
+@0 test1 : val1 ≡ Just 10
+test1 = trans (Map.insertNotChangingOthers 100 50 5 (Map.fromList ((40 , 4) ∷ (100 , 10) ∷ [])))
+        (trans (Map.insertNotChangingOthers 100 40 4 (Map.fromList ((100 , 10) ∷ [])))
+               (Map.memberAfterInsertion 100 10 Map.empty))
+
+val2 : Maybe Nat
+val2 = Map.lookup 15 firstMap
+{-# COMPILE AGDA2HS val2 #-}
+
+@0 test2 : val2 ≡ Nothing
+test2 = trans (Map.insertNotChangingOthers 15 50 5 (Map.fromList ((40 , 4) ∷ (100 , 10) ∷ [])))
+        (trans (Map.insertNotChangingOthers 15 40 4 (Map.fromList ((100 , 10) ∷ [])))
+        (trans (Map.insertNotChangingOthers 15 100 10 Map.empty)
+               (fst (Map.notMember↔Nothing 15 Map.empty)
+                      (Map.nullHasNoMembers Map.empty Map.emptyIsNull 15))))
+
+secondMap : Map Nat Nat
+secondMap = Map.delete 50 firstMap
+{-# COMPILE AGDA2HS secondMap #-}
+
+val3 : Maybe Nat
+val3 = Map.lookup 50 secondMap
+{-# COMPILE AGDA2HS val3 #-}
+
+@0 test3 : val3 ≡ Nothing
+test3 = fst (Map.notMember↔Nothing 50 secondMap)
+          (Map.notMemberAfterDeletion 50 firstMap)
+
+val4 : Maybe Nat
+val4 = Map.lookup 100 secondMap
+{-# COMPILE AGDA2HS val4 #-}
+
+@0 test4 : val4 ≡ Just 10
+test4 = trans (Map.deleteNotChangingOthers 100 50 firstMap)
+              test1
diff --git a/test/golden/AllTests.hs b/test/golden/AllTests.hs
index e38f94a7..a01f2281 100644
--- a/test/golden/AllTests.hs
+++ b/test/golden/AllTests.hs
@@ -72,4 +72,7 @@ import Issue286
 import NonClassInstance
 import Issue218
 import Issue251
+import HaskellDataOpenImport
+import HaskellDataQualifiedImport
+import Map