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To get a quad element of a quadrilateral, a diagonal is chosen; it divides the quadrilateral into two triangles. Two lines parallel to the diagonal are drawn to cut off a quarter of each triangle, leaving two small triangles and two trapezoids. The triangular pieces are rotated and together with trapezoids form the quad element, which can be translated along the diagonal in a parallel strip (P-strip).

[1] G. N. Frederickson, Dissections: Plane & Fancy, New York: Cambridge University Press, 2002 pp. 120–121. www.cs.purdue.edu/homes/gnf/book.html.