The On-Line Encyclopedia of Bongard Problems

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BP369

All points (small white circles) on one figure can be glued together to make the other figure vs. not so.

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	CROSSREFS	`See BP851 for a version where the figure must stay within the 2D plane and cannot pass through itself while being deformed.` `Adjacent-numbered pages: BP364 BP365 BP366 BP367 BP368 * BP370 BP371 BP372 BP373 BP374`
	KEYWORD	`nice, math, traditional`
	CONCEPT	`topological_transformation (info \| search),` `imagined_motion (info \| search),` `motion (info \| search)`
	WORLD	`zoom in left (figure_made_of_curves_and_quotient_by_hollow_dots)`
	AUTHOR	`Aaron David Fairbanks`

BP370

Gluing sides with the same symbols makes a sphere vs. gluing sides with the same symbols makes a torus.

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	CROSSREFS	`Adjacent-numbered pages: BP365 BP366 BP367 BP368 BP369 * BP371 BP372 BP373 BP374 BP375`
	KEYWORD	`math`
	CONCEPT	`topological_transformation (info \| search),` `3d_solid (info \| search),` `imagined_motion (info \| search),` `motion (info \| search)`
	AUTHOR	`Aaron David Fairbanks`

BP382

No knot (unknot) vs. knot.

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	COMMENTS	`To hint at the solution, left examples can be arranged in a sequence to show the unknot tying itself.`
	CROSSREFS	`Adjacent-numbered pages: BP377 BP378 BP379 BP380 BP381 * BP383 BP384 BP385 BP386 BP387`
	KEYWORD	`nice, math, anticomputer, help, traditional`
	CONCEPT	`knot (info \| search),` `topological_transformation (info \| search)`
	WORLD	`knot [smaller \| same \| bigger]`
	AUTHOR	`Aaron David Fairbanks`

BP389

Loops are entangled (in 3-D) vs. loops can be separated (in 3-D).

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	CROSSREFS	`Adjacent-numbered pages: BP384 BP385 BP386 BP387 BP388 * BP390 BP391 BP392 BP393 BP394`
	KEYWORD	`nice, precise, allsorted, contributepairs, traditional`
	CONCEPT	`knot (info \| search),` `topological_transformation (info \| search),` `imagined_motion (info \| search),` `motion (info \| search)`
	WORLD	`link_two_knots [smaller \| same \| bigger]`
	AUTHOR	`Jago Collins`

BP390

Each graph vertex is uniquely defined by its connections (the graph does not admit nontrivial automorphisms) vs. the graph admits nontrivial automorphisms.

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	CROSSREFS	`Adjacent-numbered pages: BP385 BP386 BP387 BP388 BP389 * BP391 BP392 BP393 BP394 BP395`
	KEYWORD	`precise, allsorted, notso, traditional, preciseworld`
	CONCEPT	`graph (info \| search),` `self-reference (info \| search),` `topological_transformation (info \| search),` `imagined_shape (info \| search),` `imagined_entity (info \| search)`
	WORLD	`connected_graph [smaller \| same \| bigger]`
	AUTHOR	`Jago Collins`

BP809

Figures can be transformed into one another by smooth stretching (before and after there are the same crossroad-points; there is a curve connecting points before if and only if there is a curve connecting those points after) vs. not so.

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	COMMENTS	`Left examples are topologically homeomorphic figures.` `For some examples one can imagine pulling the shape "out of" the 2d square in 3d in order to transform it, and then laying it flat back in the 2d square. See BP810 for the version where this is not allowed.`
	CROSSREFS	`Adjacent-numbered pages: BP804 BP805 BP806 BP807 BP808 * BP810 BP811 BP812 BP813 BP814`
	KEYWORD	`nice, math, unorderedpair, traditional`
	CONCEPT	`topological_transformation (info \| search)`
	WORLD	`two_figures_made_of_curves [smaller \| same \| bigger] zoom in left (two_homeomorphic_figures_made_of_curves)`
	AUTHOR	`Aaron David Fairbanks`

BP810

Figures can be transformed into one another by smooth stretching (intersection points stay constant; paths connecting those points remain), while remaining within the 2d box vs. movement out of the plane required.

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	CROSSREFS	`All examples here fit left in BP809, a version where the figures are allowed to pass through themselves while being deformed.` `Adjacent-numbered pages: BP805 BP806 BP807 BP808 BP809 * BP811 BP812 BP813 BP814 BP815`
	KEYWORD	`nice, math, unorderedpair, traditional`
	CONCEPT	`topological_transformation (info \| search)`
	WORLD	`two_homeomorphic_figures_made_of_curves [smaller \| same \| bigger]`
	AUTHOR	`Aaron David Fairbanks`

BP851

Figure with points (small white circles) can be smoothly deformed within the 2D plane without passing through itself so that all points touch to make the other figure vs. not so (movement out of the plane required).

(edit; present; nest [left/right]; search; history)

	CROSSREFS	`All examples here fit left in BP369, a version where the figure is allowed to pass through itself while being deformed.` `Adjacent-numbered pages: BP846 BP847 BP848 BP849 BP850 * BP852 BP853 BP854 BP855 BP856`
	KEYWORD	`math, traditional`
	CONCEPT	`topological_transformation (info \| search)`
	WORLD	`figure_made_of_curves_and_quotient_by_hollow_dots [smaller \| same \| bigger]`
	AUTHOR	`Aaron David Fairbanks`

BP905

Graph can be redrawn such that no edges intersect vs. not so.

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	COMMENTS	`A graph is a collection of vertices and edges. Vertices are the dots and edges are the lines that connect the dots. On the left, all edges can be redrawn (curved lines are allowed and moving vertices is allowed) such that no edges cross each other and each vertex is still connected to the same other vertices. These graphs are called planar.`
	CROSSREFS	`Adjacent-numbered pages: BP900 BP901 BP902 BP903 BP904 * BP906 BP907 BP908 BP909 BP910`
	KEYWORD	`nice, precise, allsorted, notso, math, left-null, preciseworld`
	CONCEPT	`graph (info \| search),` `topological_transformation (info \| search)`
	WORLD	`connected_graph [smaller \| same \| bigger]`
	AUTHOR	`Molly C Klenzak`

BP1102

Nodes share the same edge connections as the vertices of a cube vs. not so.

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	REFERENCE	`https://mathworld.wolfram.com/CubicalGraph.html`
	CROSSREFS	`Adjacent-numbered pages: BP1097 BP1098 BP1099 BP1100 BP1101 * BP1103 BP1104 BP1105 BP1106 BP1107`
	KEYWORD	`precise, allsorted, arbitrary, help, preciseworld`
	CONCEPT	`graph (info \| search),` `cube (info \| search),` `distinguishing_crossing_curves (info \| search),` `topological_transformation (info \| search)`
	WORLD	`connected_graph [smaller \| same \| bigger]`
	AUTHOR	`Leo Crabbe`

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