An Impossible Fork

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Blivet: an impossible fork
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Copyright © 1996-2018 Alexander Bogomolny

No one knows who invented the impossible fork that, on the left, appears to extend two rectangular prongs that, on the right, metamorphose into three cylinders. It was known at the Moscow State University in the late 1960s. Martin Gardner refers to it as blivet and elsewhere I came across the term the Devil's pitchfork.

Structural Constellation is another impossible figure as is an Impossible Frame.


  1. M. Gardner, Mathematical Circus, Vintage Books, 1981
  2. A. Seckel, More Optical Illusions, Carlton Books, 2002 (#137)
  3. R. N. Shepard, Mind Sights, W. H. Freeman and Company, 1990

Related material

  • There are really impossible things...
  • An Impossible Frame
  • Structural Constellation
  • Squaring a circle
  • Trisecting an angle (in general)
  • Doubling a cube
  • A puzzle of identical twins
  • Geometric construction with the straightedge alone
  • |Contact| |Front page| |Contents| |Geometry| |Impossible|

    Copyright © 1996-2018 Alexander Bogomolny