Left Bongard Problems do not have to sort all relevant examples; if they would leave some border cases unsorted, it just has to be clear precisely which examples those would be.

Often a precise divide between values on a spectrum comes from intuitively "crossing a threshold." For example, there is an intuitive threshold between acute and obtuse angles. Two sides of a Bongard Problem on opposite ends of a threshold, coming close to it, are interpreted as having precise divide between sides, right up against that threshold.

See BP508 for the version with links to pages on the OEBP instead of images of Bongard Problems.

Adjacent-numbered pages:
BP871 BP872 BP873 BP874 BP875  *  BP877 BP878 BP879 BP880 BP881

hard, notso, challenge, meta (see left/right), miniproblems, creativeexamples, assumesfamiliarity, structure, presentationinvariant

bpimage_shapes [smaller | same | bigger]
zoom in left (bpimage_shapes_exact_sort)

Aaron David Fairbanks

One left and one right example with each solution are shown for help.

This BP is fuzzy for multiple reasons. How obvious it is that an example fits a rule is subjective. Also, somebody could read the simplicity of all included examples as part of a Bongard Problem's solution. For example, the more obvious version of "square number of dots vs. non-square number of dots" could be interpreted as "square small number of dots arranged in easy-to-read way vs. non-square small number of dots arranged in easy-to-read way."

Whether this Bongard Problem solution would categorize an image of itself left or right depends on the difficulty of the solutions of the mini-Problems.

See keyword help.

See keyword hardsort.

Adjacent-numbered pages:
BP889 BP890 BP891 BP892 BP893  *  BP895 BP896 BP897 BP898 BP899

fuzzy, abstract, notso, subjective, meta (see left/right), miniproblems, creativeexamples, presentationmatters, assumesfamiliarity, structure, contributepairs

boxes_bpimage_three_per_side [smaller | same | bigger]

Aaron David Fairbanks

Another solution is that right examples can be folded down flat onto one isosceles triangle while left examples cannot.

All examples in this Problem feature four isosceles triangles connected by corners and/or edges.

This was conceived as a false solution for BP898.

Adjacent-numbered pages:
BP892 BP893 BP894 BP895 BP896  *  BP898 BP899 BP900 BP901 BP902

precise, allsorted, notso, traditional, preciseworld

[smaller | same | bigger]

Molly C Klenzak, Aaron David Fairbanks

Which two sides are the long sides and which side is the short side, or equivalently which angles are the wider angles and which angle is the narrower angle, is the only relevant information to consider for each triangle. Triangles are all assumed isosceles and congruent to one another.

All examples in this Problem feature four of these triangles connected by corners and/or edges.

BP897 was conceived as a false solution for this.

Adjacent-numbered pages:
BP893 BP894 BP895 BP896 BP897  *  BP899 BP900 BP901 BP902 BP903

hard, precise, allsorted, notso, math, preciseworld

[smaller | same | bigger]

Molly C Klenzak

Although this Bongard Problem is self-referential, it's only because of the specific phrasing of the solution. "BP902 vs. anything else" would also work. The number 902 could have been chosen coincidentally.

See BP953, BP959.

Adjacent-numbered pages:
BP897 BP898 BP899 BP900 BP901  *  BP903 BP904 BP905 BP906 BP907

notso, meta (see left/right), links, left-self, left-narrow, left-finite, left-full, right-null, right-it, invalid, experimental, funny

everything [smaller | same]
zoom in left (bp902)

Leo Crabbe

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.

Adjacent-numbered pages:
BP900 BP901 BP902 BP903 BP904  *  BP906 BP907 BP908 BP909 BP910

nice, precise, allsorted, notso, math, left-null, preciseworld

connected_graph [smaller | same | bigger]

Molly C Klenzak

Adjacent-numbered pages:
BP910 BP911 BP912 BP913 BP914  *  BP916 BP917 BP918 BP919 BP920

less, notso, spectrum, number, example, left-null, impossible, experimental

dots [smaller | same | bigger]

Jago Collins

Adjacent-numbered pages:
BP923 BP924 BP925 BP926 BP927  *  BP929 BP930 BP931 BP932 BP933

notso, math, traditional

Aaron David Fairbanks

"Full overlapping not allowed" means you cannot overlay an image onto itself without moving it; if this were allowed all images would be sorted on the left. The copies can be moved around (translated) in 2D but can not be flipped or rotated.

There are examples on the right drawn with thick lines, and these could be created by copying an image with slightly thinner lines and moving it over a tiny amount. If you fix this issue by saying "the copy has to be moved over more than a tiny amount" then the Bongard Problem is perfect but not precise, but if you fix this issue by saying "interpret the figures as made up of (infinitesimally) thin lines" then it's precise but not perfect. - Aaron David Fairbanks, Jun 17 2023

Adjacent-numbered pages:
BP941 BP942 BP943 BP944 BP945  *  BP947 BP948 BP949 BP950 BP951

nice, notso, creativeexamples

Leo Crabbe

Examples on the left are also known as "Dyck words".

https://en.wikipedia.org/wiki/Dyck_language

Adjacent-numbered pages:
BP951 BP952 BP953 BP954 BP955  *  BP957 BP958 BP959 BP960 BP961

easy, nice, precise, allsorted, unwordable, notso, sequence, traditional, inductivedefinition, preciseworld, left-listable, right-listable

Aaron David Fairbanks