--- /dev/null
+.. _diagonal_inversion_of_elements_page:
+
+***********************************
+Diagonal inversion of two triangles
+***********************************
+
+In MESH you can inverse the diagonal (edge) of a pseudo-quadrangle
+formed by two neighboring triangles with one common edge.
+
+*To inverse the diagonal:*
+
+#. From the **Modification** menu choose the **Diagonal inversion** item or click *"Diagonal Inversion"* |img| button in the toolbar.
+
+.. |img| image:: ../images/image70.png
+
+The following dialog box shall appear:
+
+ .. image:: ../images/diagonalinversion.png
+ :align: center
+
+#. Enter IDs of nodes forming the required edge in the **Edge** field (the node IDs must be separated by dashes) or select this edge in the 3D viewer.
+#. Click the **Apply** or **Apply and Close** button.
+
+ .. image:: ../images/image38.jpg
+ :align: center
+
+ .. centered::
+ The selected edge
+
+ .. image:: ../images/image36.jpg
+ :align: center
+
+ .. centered::
+ The inverted edge
+
+**See Also** a sample TUI Script of a :ref:`tui_diagonal_inversion` operation.
+
+