print illustrates the "impossible triangle" described by the British
mathematician Roger Penrose in a 1958 article on visual illusion:
"Here is a perspective drawing, each part of which is accepted as
representing a three-dimensional, rectangular structure. The lines
of the drawing are, however, connected in such a manner as to
reproduce an impossibility. As the eye pursues the lines of the
figure, sudden changes in the interpretation of distance of the
object from the observer are necessary."