diff --git a/MOBasis/MOBasis.mli b/MOBasis/MOBasis.mli
index 3f8a0bc..d918cfc 100644
--- a/MOBasis/MOBasis.mli
+++ b/MOBasis/MOBasis.mli
@@ -73,6 +73,15 @@ val of_hartree_fock : HartreeFock.t -> t
 val of_mo_basis : Simulation.t -> t -> t
 (** Project the MOs of the other basis on the current one. *)
 
+
+val mo_matrix_of_ao_matrix : mo_coef:Mat.t -> Mat.t -> Mat.t
+(** Build a matrix in MO basis from a matrix in AO basis. *)
+
+val ao_matrix_of_mo_matrix : mo_coef:Mat.t ->  ao_overlap:Mat.t -> Mat.t -> Mat.t 
+(** Build a matrix in AO basis from a matrix in MO basis. *)
+
+
+
 (** {1 Printers} *)
 
 val pp : ?start:int -> ?finish:int -> Format.formatter -> t -> unit