Abstract
Two comments suggest possible documentation for two impossible figures, the Penrose triangle and Necker's cube.
References
1.
Escher
M. C.
The graphic work of M. C. Escher . (2nd ed. ) London : Oldbourne , 1961 .
2.
Molins
J. V.
Some thoughts on impossible figures . Perceptual and Motor Skills , 1991 , 73 , 107 –114 .
3.
Necker
L. A.
Betrachtung gezeichneter Figuren . Poggendorffs Annalen der Physik , 1833 , 27 , 502 .
4.
Penrose
L. S.
Penrose
R.
Impossible objects: A special type of illusion . British Journal of Psychology , 1958 , 49 , 31 –33 .