diff --git a/EgtGeomKernel.rc b/EgtGeomKernel.rc
index b490063..6716bf9 100644
Binary files a/EgtGeomKernel.rc and b/EgtGeomKernel.rc differ
diff --git a/Polygon3d.cpp b/Polygon3d.cpp
index 997788b..473348e 100644
--- a/Polygon3d.cpp
+++ b/Polygon3d.cpp
@@ -26,6 +26,14 @@ Polygon3d::Clear( void)
    return true ;
 }
 
+//----------------------------------------------------------------------------
+bool
+Polygon3d::ClearSides( void)
+{
+   m_vVert.clear() ;
+   return true ;
+}
+
 //----------------------------------------------------------------------------
 bool
 Polygon3d::FromRectangle( double dDimX, double dDimY)
@@ -181,7 +189,7 @@ Polygon3d::Trim( const Plane3d& plPlane, bool bInVsOut, bool bOnEq)
 bool
 Polygon3d::Trim( const Polygon3d& plyOther, bool bInVsOut, bool bOnEq)
 {
-   if ( GetSideCount() == 0  ||  plyOther.GetSideCount() == 0)
+   if ( GetSideCount() == 0  ||  ! plyOther.IsValid())
       return true ;
    return Trim( plyOther.m_Plane, bInVsOut, bOnEq) ;
 }
diff --git a/StmStandard.cpp b/StmStandard.cpp
index b32142e..d023e1d 100644
--- a/StmStandard.cpp
+++ b/StmStandard.cpp
@@ -170,7 +170,7 @@ GetSurfTriMeshPlaneInBox( const Plane3d& plPlane, const BBox3d& b3Box)
   // creo la trimesh con questo contorno
    PtrOwner<ISurfTriMesh> pStm( CreateSurfTriMesh()) ;
    if ( IsNull( pStm)  ||  ! pStm->CreateByFlatContour( Polyg.GetPolyLine()))
-      return false ;
+      return nullptr ;
   // restituisco la superficie
    return Release( pStm) ;
 }