Two shapes can tessellate the plane together vs. not so.
Two shapes can tessellate the plane vs. not so.
Two objects can tessellate the plane vs. not so.
The two objects can tessellate the plane together vs. not so.
Leo Crabbe
Bongard Problems with "world" finitely many closed thin non-crossing black 2D shape outlines allowed to nest vs. other Bongard Problems.
Aaron David Fairbanks