Restrictions

The following requirements must be fulfilled for the 'special webs'.

1. The web must have four boundaries.

2. The first boundary must be a frame curve.

3. The 'free' side, the location of which is defined by measures, must be boundary number 3.

4. Boundaries 2 and 4 must be straight lines (which, however, may result from plane intersecting panels, ).

5. Allowed geometry types are 102, 103 and 104.