diff --git a/Basis/Basis.ml b/Basis/Basis.ml
index f3488cb..6ff464b 100644
--- a/Basis/Basis.ml
+++ b/Basis/Basis.ml
@@ -18,7 +18,7 @@ let of_nuclei_and_general_basis n b =
             and coef = Array.map (fun General_basis.{exponent ; coefficient} ->
                 coefficient) shell
             in
-            Contracted_shell.create ~expo ~coef ~totAngMom ~center ~index:0)
+            Contracted_shell.make ~expo ~coef ~totAngMom ~center ~index:0)
       ) n
     |> Array.to_list
     |> Array.concat
diff --git a/Basis/Contracted_shell.ml b/Basis/Contracted_shell.ml
index 2b294ff..a7f8fdc 100644
--- a/Basis/Contracted_shell.ml
+++ b/Basis/Contracted_shell.ml
@@ -1,17 +1,8 @@
 open Util
 open Constants
+open Contracted_shell_type 
 
-type t = {
-  expo      : float array;
-  coef      : float array;
-  center    : Coordinate.t;
-  totAngMom : Angular_momentum.t;
-  size      : int;
-  norm_coef : float array;
-  norm_coef_scale : float array;
-  index    : int;
-  powers   : Zkey.t array;
-}
+type t = Contracted_shell_type.t
 
 let size a = a.size
 let expo a i = a.expo.(i)
@@ -21,10 +12,9 @@ let totAngMom a = a.totAngMom
 let norm_coef a i = a.norm_coef.(i)
 let norm_coef_scale a  = a.norm_coef_scale
 let index a  = a.index
-let with_index a i = { a with index = i }
+let with_index = Contracted_shell_type.with_index
 let powers a = a.powers
 
-
 let to_string s =
   let coord =
     Coordinate.to_Bohr s.center
@@ -72,24 +62,5 @@ let compute_norm_coef expo totAngMom =
   Array.map (fun x -> let f a = x *. (factor a) in f) expo
 
 
-let create ~index ~expo ~coef ~center ~totAngMom =
-  assert (Array.length expo = Array.length coef);
-  assert (Array.length expo > 0);
-  let norm_coef_func =
-    compute_norm_coef expo totAngMom
-  in
-  let powers =
-    Angular_momentum.zkey_array (Angular_momentum.Singlet totAngMom) 
-  in
-  let norm_coef =
-    Array.map (fun f -> f [| Angular_momentum.to_int totAngMom ; 0 ; 0 |])  norm_coef_func
-  in
-  let norm_coef_scale = 
-    Array.map (fun a ->
-      (norm_coef_func.(0) (Zkey.to_int_array ~kind:Zkey.Kind_3 a)) /. norm_coef.(0)
-    ) powers
-  in
-  { index ; expo ; coef ; center ; totAngMom ; size=Array.length expo ; norm_coef ;
-    norm_coef_scale ; powers }
-
+let make = Contracted_shell_type.make
 
diff --git a/Basis/Contracted_shell.mli b/Basis/Contracted_shell.mli
index b0bdd46..55bf153 100644
--- a/Basis/Contracted_shell.mli
+++ b/Basis/Contracted_shell.mli
@@ -1,4 +1,4 @@
-type t
+type t = Contracted_shell_type.t
 
 
 (** Returns the number of contracted Gaussians *)
@@ -46,7 +46,7 @@ val powers : t -> Zkey.t array
 val to_string : t -> string
 
 (** Creates a contracted shell *)
-val create :
+val make :
   index:int ->
   expo:float array ->
   coef:float array ->
diff --git a/Utils/Positive_float.ml b/Utils/Positive_float.ml
index 6f3faea..fbf46c0 100644
--- a/Utils/Positive_float.ml
+++ b/Utils/Positive_float.ml
@@ -4,9 +4,11 @@ let of_float x =
   assert ( x >= 0. );
   x
 
-let to_float x = x
+external to_float : t -> float = "%identity"
 
-let to_string x = string_of_float @@ to_float x
+let to_string x =
+  let f = to_float x in string_of_float f
 
-let of_string x = of_float @@ float_of_string x
+let of_string x =
+ let f = float_of_string x in of_float f
 
diff --git a/Utils/Positive_float.mli b/Utils/Positive_float.mli
index b0b6e73..2d3d60b 100644
--- a/Utils/Positive_float.mli
+++ b/Utils/Positive_float.mli
@@ -1,4 +1,4 @@
-type t
+type t = private float
 val of_float : float -> t
 val to_float : t -> float
 val to_string : t -> string