All examples in this problem include three or fewer outlines of circles, (near-square) quadrilaterals and (non-skinny) triangles.
M. M. Bongard, Pattern Recognition, Spartan Books, 1970, p. 221.
Adjacent-numbered pages: BP17 BP18 BP19 BP20 BP21  *  BP23 BP24 BP25 BP26 BP27
finished, traditional, bongard
circle_triangle_squareish_outlines [smaller | same | bigger]
Mikhail M. Bongard