+\ref tui_propagation "Propagation hypothesis" operation
+
+<h2>Quadrangle Preference</h2>
+
+This additional hypothesis can be used together with Quadrangle (Mapping) and Netgen 2D
+algorithms.
+
+It allows Netgen 2D to build quadrangular meshes at any conditions.
+
+It allows Quadrangle (Mapping) to build quadrangular meshes even if the number
+of nodes at the opposite edges of a meshed face is not equal,
+otherwise this mesh will contain some triangular elements.
+<br>
+This hypothesis has one restriction on its work: the total quantity of
+segments on all four sides of the face must be even (divisible by 2).
+
+<h2>Triangle Preference</h2>
+
+This additional hypothesis can be used only together with Quadrangle (Mapping)
+algorithm. It allows to build triangular mesh faces in the refinement
+area if the number of nodes at the opposite edges of a meshed face is not equal,
+otherwise refinement area will contain some quadrangular elements.
+