diff --git a/MMVII/include/MMVII_Mappings.h b/MMVII/include/MMVII_Mappings.h
index 9d8e6dcfd5..4937dc8126 100644
--- a/MMVII/include/MMVII_Mappings.h
+++ b/MMVII/include/MMVII_Mappings.h
@@ -29,7 +29,16 @@
 namespace MMVII
 {
 template <class Type,const int Dim> class cDataBoundedSet ;
+template <class Type,const int DimIn,const int DimOut> class cMapping;
 template <class Type,const int DimIn,const int DimOut> class cDataMapping;
+template <class Type,const int Dim> class cDataInvertibleMapping ;// :  public cDataMapping<Type,Dim,Dim>
+template <class Type,const int Dim> class cDataIterInvertMapping ;// :  public cDataInvertibleMapping<Type,Dim>
+template <class Type,const int Dim> class cDataIIMFromMap ; // : public cDataIterInvertMapping<Type,Dim>
+
+template <class Type,const int Dim> class cMappingIdentity ; // :  public cDataMapping<Type,Dim,Dim>
+template <class Type,const int DimIn,const int DimOut> class cDataMapCalcSymbDer ;// : public cDataMapping<Type,DimIn,DimOut>
+template <class cMapElem,class cIMapElem> class cInvertMappingFromElem ;// :  public cDataInvertibleMapping<typename cMapElem::TheType,cMapElem::TheDim>
+{   
 
 /** \file MMVII_Mappings.h
     \brief contain interface class for continuous mapping
@@ -448,13 +457,19 @@ template <class cMapElem,class cIMapElem> class cInvertMappingFromElem :  public
 };
 
 /**
-     We have a set of function F1,  .. Fp     R^k => R ^n
-
+     We have a set of function F1,  .. Fp     R^k => R ^n, we want to estimate F  as a linear combination:
+           F =  Sum   Al Fl 
      We have samples      Km , Nm 
+     We want to solve by  lest square  :   F (Km) = Nm
 
-     We want to solve by  lest square  :
-            Sum   Al Fl (Km) = Nm
+     The computation is not optimized (not parallized) as it would add a complexity important for
+     a probable low gain :
+         * there is not so many samples
+         * we dont compute the derivative
+         * the filling of matrix is however a cost not parallized
 */
+
+
 template <class Type,const int  DimIn,const int DimOut> class cLeastSqComputeMaps
 {
      public :
@@ -464,6 +479,7 @@ template <class Type,const int  DimIn,const int DimOut> class cLeastSqComputeMap
          typedef  std::vector<tPtOut>         tVecOut;
 
          cLeastSqComputeMaps(size_t aNbFunc);
+         /// Add obs 
          void AddObs(const tPtIn & aPt,const tPtOut & aValue,const tPtOut & aPds);
          void AddObs(const tPtIn & aPt,const tPtOut & aValue,const Type & aPds);
          void AddObs(const tPtIn & aPt,const tPtOut & aValue);
diff --git a/MMVII/src/Mappings/cLeastSqComputeMaps.cpp b/MMVII/src/Mappings/cLeastSqComputeMaps.cpp
index 00cce7bf3f..21cc70bfa8 100644
--- a/MMVII/src/Mappings/cLeastSqComputeMaps.cpp
+++ b/MMVII/src/Mappings/cLeastSqComputeMaps.cpp
@@ -47,6 +47,19 @@ template <class Type,const int  DimIn,const int DimOut>
      AddObs(aPtIn,aValue,1.0);
 }
 
+/* ============================================= */
+/*      cLeastSqCompMapCalcSymb<Type>            */
+/* ============================================= */
+
+
+template <class Type,const int DimIn,const int DimOut>
+    class cLeastSqCompMapCalcSymb : public cLeastSqCompMapCalcSymb<Type,DimIn,DimOut>
+{
+    public :
+      typedef typename NS_SymbolicDerivative::cCalculator<Type> tCalc;
+};
+/*
+*/
 
 /* ===================================================== */
 /* =====              INSTANTIATION                ===== */
@@ -56,6 +69,7 @@ template <class Type,const int  DimIn,const int DimOut>
 template class cLeastSqComputeMaps<TYPE,DIMIN,DIMOUT>;
 
 INSTANTIATE_LSQMAP(tREAL8,3,2)
+INSTANTIATE_LSQMAP(tREAL8,2,2)
 
 /*
 #define INSTANTIATE_OPMulMatVect(T1,T2)\