+The algorithm can propagate 2D mesh not only between horizontal
+(i.e. base and top) faces of one prism but also between faces of prisms
+organized in a stack and between stacks sharing prism sides.
+
+\image html prism_stack.png "Prism stacks"
+This picture shows four neighboring prism stacks, each comprising two prisms.
+The shown sub-mesh is used by the algorithm to mesh
+all eight prisms in the stacks.
+
+To use <em>Extrusion 3D</em> algorithm you need to assign algorithms
+and hypotheses of lower dimensions as follows.
+(A sample picture below shows algorithms and hypotheses used to
+mesh a cylinder with prismatic volumes).
+
+\image html prism_needs_hyps.png
+
+The \b Global algorithms and hypotheses to be chosen at
+\ref create_mesh_anchor "Creation of a mesh object" are:
+<ul>
+<li> 1D algorithm and hypothesis that will be applied for meshing
+ (logically) vertical edges of the prism (which connect the top and the
+ base faces of the prism). In the sample picture above these are
+ "Regular_1D" algorithm and "Number of Segments" hypothesis named "Vertical
+ Nb. Segments".</li>
+</ul>
+
+The \b Local algorithms and hypotheses to be chosen at
+\ref constructing_submeshes_page "Construction of sub-meshes" are:
+<ul>
+ <li> 1D and 2D algorithms and hypotheses that will be applied for
+ meshing the top and the base prism
+ \ref submesh_shape_section "faces". These faces can be meshed
+ with any type of 2D elements: quadrangles, triangles, polygons or
+ their mix. It is enough to define a sub-mesh on either the top or
+ the base face. In the sample picture above, "NETGEN_1D2D"
+ algorithm meshes "bottom disk" face with triangles. (1D algorithm
+ is not assigned as "NETGEN_1D2D" does not require divided edges to
+ create a 2D mesh.)
+ </li>
+ <li> Optionally you can define a 1D sub-mesh on some vertical
+ \ref submesh_shape_section "edges" of stacked prisms, which will
+ override the global 1D hypothesis mentioned above. In the <b>Prism
+ stacks</b> picture, the vertical division is not equidistant on
+ the whole length because a "Number Of Segments" hypothesis with
+ Scale Factor=3 is assigned to the highlighted edge.
+</li></ul>
+
+If <em>Extrusion 3D</em> algorithm is assigned to a sub-mesh in a mesh
+with multiple sub-meshes, the described above approach may not work as
+expected. For example the bottom face may be meshed by other algorithm
+before <em>Extrusion 3D</em> have a chance to project a mesh from the
+base face. This thing can happen with vertical edges as well. All
+these can lead to either a meshing failure or to an incorrect meshing.
+
+In such a case, it's necessary to explicitly define algorithms
+that <em>Extrusion 3D</em> implicitly applies in a simple case:
+- assign \ref projection_1D2D algorithm to the top face and
+- assign a 1D algorithm to a group of all vertical edges.
+
+\image html image157.gif "Prism with Extrusion 3D meshing. Vertical division is different on neighbor edges because several local 1D hypotheses are assigned."
+
+\sa a sample TUI Script of
+\ref tui_prism_3d_algo "Use Extrusion 3D meshing algorithm".
