The On-Line Encyclopedia of Bongard Problems

Search: author:Leo Crabbe

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Shape can be maneuvered around the corner vs. not so.

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	REFERENCE	`https://en.wikipedia.org/wiki/Moving_sofa_problem`
	CROSSREFS	`Adjacent-numbered pages: BP845 BP846 BP847 BP848 BP849 * BP851 BP852 BP853 BP854 BP855`
	KEYWORD	`nice, precise, physics, creativeexamples, proofsrequired, left-narrow, right-narrow, dithering`
	CONCEPT	`rotation_required (info \| search),` `imagined_motion (info \| search),` `physically_fitting (info \| search)`
	AUTHOR	`Leo Crabbe`

Evokes the idea of symmetry vs. not so.

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	COMMENTS	`Or, perhaps more concretely, "Depiction of object with some symmetry (invariance under transformation) vs. depiction of object with no simple symmetries."`
	CROSSREFS	`Adjacent-numbered pages: BP842 BP843 BP844 BP845 BP846 * BP848 BP849 BP850 BP851 BP852`
	KEYWORD	`nice, fuzzy, abstract, math, concept, collective, dithering`
	CONCEPT	`symmetry (info \| search)`
	AUTHOR	`Leo Crabbe`

Dot's position within square is center of square's position within panel vs. not so.

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	COMMENTS	`All examples in this problem are dots inside square outlines.`
	CROSSREFS	`Similar to BP1122 (the "fractal" version).` `Adjacent-numbered pages: BP813 BP814 BP815 BP816 BP817 * BP819 BP820 BP821 BP822 BP823`
	KEYWORD	`nice, notso, boundingbox, absoluteposition`
	CONCEPT	`bounding_box (info \| search),` `self-reference (info \| search),` `center (info \| search),` `distance_from_center (info \| search)`
	WORLD	`point_inside_square [smaller \| same \| bigger]`
	AUTHOR	`Leo Crabbe`

Cross section of a cylinder vs. not cross section of a cylinder

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	CROSSREFS	`Adjacent-numbered pages: BP811 BP812 BP813 BP814 BP815 * BP817 BP818 BP819 BP820 BP821`
	KEYWORD	`precise, notso, stretch, unstable, perfect`
	CONCEPT	`cross_section (info \| search)`
	WORLD	`fill_shapes [smaller \| same \| bigger]`
	AUTHOR	`Leo Crabbe`

Triangular number of dots vs. non-triangular number of dots

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	COMMENTS	`All examples in this Problem are groups of black dots.` `The nth triangular number is the sum over the natural numbers from 1 to n, where n > 0. Note: 0 is the 0th triangular number. The first few triangular numbers are 0, 1, 3 (= 1+2) and 6 (= 1+2+3)`
	CROSSREFS	`Adjacent-numbered pages: BP564 BP565 BP566 BP567 BP568 * BP570 BP571 BP572 BP573 BP574`
	KEYWORD	`nice, precise, allsorted, notso, number, math, left-narrow, left-null, help, preciseworld`
	WORLD	`dots [smaller \| same \| bigger]`
	AUTHOR	`Leo Crabbe`

Discrete points intersecting boundary of convex hull vs. connected segment intersecting boundary of convex hull

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	COMMENTS	`If a "string" is wound tightly around the shape, does one of its segments lie directly on the shape?` `All examples in this Problem are connected line segments or curves.` `We are taking lines here to be infinitely thin, so that if the boundary of the convex hull intersects the endpoint of a line exactly it is understood that they meet at 1 point.`
	CROSSREFS	`Adjacent-numbered pages: BP559 BP560 BP561 BP562 BP563 * BP565 BP566 BP567 BP568 BP569`
	EXAMPLE	`Imagine wrapping a string around the pointed star. This string would take the shape of the boundary of the star's convex hull (a regular pentagon), and would only touch the star at the end of each of its 5 individual tips, therefore the star belongs on the left.`
	KEYWORD	`hard, nice, allsorted, solved, perfect`
	AUTHOR	`Leo Crabbe`

Cross section of a cube vs. not cross section of a cube

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	COMMENTS	`All examples are solid black shapes.` `This problem is absurdly hard. It makes a good extreme example. - Aaron David Fairbanks, Nov 23 2020`
	CROSSREFS	`Adjacent-numbered pages: BP554 BP555 BP556 BP557 BP558 * BP560 BP561 BP562 BP563 BP564`
	KEYWORD	`hard, precise, allsorted, notso, stretch, challenge, left-narrow, perfect`
	CONCEPT	`cube (info \| search),` `cross_section (info \| search)`
	WORLD	`fill_shape [smaller \| same \| bigger]`
	AUTHOR	`Leo Crabbe`

Point sequence that is increasing or decreasing in height vs. point sequence that alternates in height

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	COMMENTS	`All examples in this Problem are groups of 3 dots.` `Any example where 2 adjacent dots have the same height would be ambiguously sorted.`
	CROSSREFS	`Adjacent-numbered pages: BP553 BP554 BP555 BP556 BP557 * BP559 BP560 BP561 BP562 BP563`
	EXAMPLE	`Reading from right to left in the first box on the left hand side: the 2nd dot is higher than the 1st, and the 3rd is higher than the 2nd, so the sequence of dots is strictly increasing in height.`
	KEYWORD	`nice, precise, antihuman, orderedtriplet, preciseworld`
	CONCEPT	`coordinate (info \| search)`
	WORLD	`three_points [smaller \| same \| bigger]`
	AUTHOR	`Leo Crabbe`

Equal horizontal length vs. not

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	COMMENTS	`All examples in this Problem are pairs of straight line segments.` `This problem communicates the idea of projected distance, in this case from 2D to 1D (x-axis).`
	CROSSREFS	`Adjacent-numbered pages: BP552 BP553 BP554 BP555 BP556 * BP558 BP559 BP560 BP561 BP562`
	KEYWORD	`nice, precise, allsorted, stretch, perfect, unorderedpair, preciseworld`
	CONCEPT	`projection (info \| search)`
	WORLD	`two_segments [smaller \| same \| bigger]`
	AUTHOR	`Leo Crabbe`

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