The On-Line Encyclopedia of Bongard Problems

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Unstable balance vs. not

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	REFERENCE	`https://en.wikipedia.org/wiki/Stability_theory`
	CROSSREFS	`Adjacent-numbered pages: BP546 BP547 BP548 BP549 BP550 * BP552 BP553 BP554 BP555 BP556`
	EXAMPLE	`The classic example is a pendulum with a solid rod (instead of a string) which has a stable balance point at the bottom of its swing, where if you move the pendulum slightly it will swing back towards that balanced state. However, theoretically the pendulum can also be balanced pointing directly up. In this case, if you move the pendulum slightly it will swing down away from that upwards balanced state.`
	KEYWORD	`updown, rotate, physics, anticomputer, perfect`
	CONCEPT	`tumbles_or_stays_put (info \| search),` `gravity (info \| search)`
	AUTHOR	`Jago Collins`

Black and white photograph versus drawing.

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	COMMENTS	`Although the images here are related to culture (BP521^left), the solution of this Bongard Problem is about the visual style of the images.`
	CROSSREFS	`Adjacent-numbered pages: BP550 BP551 BP552 BP553 BP554 * BP556 BP557 BP558 BP559 BP560`
	KEYWORD	`less, culture, experimental`
	WORLD	`zoom in left (black_and_white_photograph)`
	AUTHOR	`Aaron David Fairbanks`

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`

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`

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`

There exists a closed trail that hits each edge exactly once vs. not so.

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	COMMENTS	`Left examples are called "Eulerian graphs."` `A connected graph is Eulerian if and only if each vertex is incident to an even number of edges.`
	CROSSREFS	`Adjacent-numbered pages: BP555 BP556 BP557 BP558 BP559 * BP561 BP562 BP563 BP564 BP565`
	KEYWORD	`precise, allsorted, math, traditional, preciseworld`
	CONCEPT	`graph (info \| search),` `distinguishing_crossing_curves (info \| search),` `all (info \| search),` `even_odd (info \| search),` `existence (info \| search)`
	WORLD	`connected_graph [smaller \| same \| bigger]`
	AUTHOR	`Aaron David Fairbanks`

There exists a closed trail that hits each vertex exactly once vs. not so.

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	COMMENTS	`Left examples are called "Hamiltonian graphs."`
	CROSSREFS	`Adjacent-numbered pages: BP557 BP558 BP559 BP560 BP561 * BP563 BP564 BP565 BP566 BP567`
	KEYWORD	`math, traditional`
	CONCEPT	`graph (info \| search),` `distinguishing_crossing_curves (info \| search)`
	WORLD	`connected_graph [smaller \| same \| bigger]`
	AUTHOR	`Aaron David Fairbanks`

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`

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`

Shape outlines that aren't triangles vs. black shapes that aren't squares.

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	COMMENTS	`An example of an overriddensolution.`
	CROSSREFS	`Adjacent-numbered pages: BP565 BP566 BP567 BP568 BP569 * BP571 BP572 BP573 BP574 BP575`
	KEYWORD	`less, example, overriddensolution, experimental, funny, neither`
	WORLD	`outline_or_fill_shape [smaller \| same \| bigger]`
	AUTHOR	`Aaron David Fairbanks`

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