  Kokotsakis studied the following problem in 1932: Given is a rigid closed
polygonal line (planar or non-planar), which is surrounded by a polyhedral
strip, where at each polygon vertex three faces meet. Determine the geometries
of these closed strips with a continuous mobility. On the one side, we
generalize this problem by allowing the faces, which are adjacent to polygon
line-segments, to be skew; i.e to be non-planar. But on the other side, we
restrict to the case where the four angles associated with each polygon vertex
fulfill the so-called isogonality condition that both pairs of opposite angles
are equal or supplementary. In more detail, we study the case where the
polygonal line is a skew quad, as this corresponds to a (3x3) building block of
a so-called V-hedra composed of skew quads. The latter also gives a positive
answer to a question posed by Robert Sauer in his book of 1970 whether
continuous flexible skew quad surfaces exist.
