Cubism:

In their theoretical rules, the Cubist architects expressed the requirement of dynamism, which would surmount the matter and calm contained in it, through a creative idea, so that the result would evoke feelings of dynamism and expressive plasticity in the viewer. This should be achieved by shapes derived from pyramids, cubes and prisms, by arrangements and compositions of oblique surfaces, mainly triangular, sculpted facades in protruding crystal-like units, reminiscent of the so-called diamond cut, or even cavernous that are reminiscent of the late Gothic architecture. In this way, the entire surfaces of the facades including even the gables and dormers are sculpted. The grilles as well as other architectural ornaments attain a three-dimensional form. Thus, new forms of windows and doors were also created, e. g. hexagonal windows. Czech Cubist architects also designed Cubist furniture.

Please answer a question about this article. If the question is unanswerable, say "unanswerable". What's  window shapes di Czech Cubist architects use?
hexagonal