Left-sorted Bongard Problems have the keyword "left-couldbe" on the OEBP.

Right-sorted Bongard Problems have the keyword "right-couldbe".

In a "couldbe" Bongard Problem, some relevant information is left out by the way objects are displayed. Solutions to "left-couldbe" BPs sound like "Could be a ___ vs. definitely not a ___" (and vice versa for "right-couldbe" BPs.)

To put it in mathematical jargon, there is a "projection" function from objects to pictures, such that objects satisfying property X are mapped to the same picture as objects not satisfying property X. Sorted on the "couldbe" side is the image (under projection) of the collection of objects satisfying property X.

Furthermore, usually X is a relatively narrow criterion, so that most objects do not satisfy it (see keywords left-narrow and right-narrow), and all pictures are in the image (under projection) of the collection of objects not satisfying property X.

Consider BP525, "Cropped image of a circle vs. not so." None of the left-hand examples are definitely an image of a circle, but they fit left because nothing indicates that they are not an image of a circle. A more pedantic solution to this Bongard Problem would be "There is a way of cropping a circle that gives this image vs. there isn't."

See also the keyword seemslike, where neither side can be confirmed.

Either "left-couldbe" or "right-couldbe" implies notso.

Although the descriptions of "left-couldbe" and "right-couldbe" sound similar to left-unknowable and right-unknowable, they are not the same. It is the difference between a clear absence of information and perpetual uncertainty about whether there is more information to be found.

"Left-couldbe" is usually left-narrow and "right-couldbe" usually right-narrow.

Adjacent-numbered pages:
BP1154 BP1155 BP1156 BP1157 BP1158  *  BP1160 BP1161 BP1162 BP1163 BP1164

dual, meta (see left/right), links, keyword, side, viceversa

Leo Crabbe

The triangles vary in size in order to make the solution clearly about quantity, not "total mass".

Adjacent-numbered pages:
BP1203 BP1204 BP1205 BP1206 BP1207  *  BP1209 BP1210 BP1211 BP1212 BP1213

stub, precise, spectrum, dual, handed, leftright, traditional

Aaron David Fairbanks

Adjacent-numbered pages:
BP1208 BP1209 BP1210 BP1211 BP1212  *  BP1214 BP1215 BP1216 BP1217 BP1218

stub, dual, handed, leftright, updown, rotate, stretch, left-narrow, right-narrow, traditional, both

Aaron David Fairbanks

BP1217 has the same solution but rotated a quarter-turn counter-clockwise.

Adjacent-numbered pages:
BP1209 BP1210 BP1211 BP1212 BP1213  *  BP1215 BP1216 BP1217 BP1218 BP1219

stub, dual, handed, leftright, traditional

Aaron David Fairbanks

BP1218 is "arrow pointing north-west vs. arrow pointing elsewhere".

Adjacent-numbered pages:
BP1211 BP1212 BP1213 BP1214 BP1215  *  BP1217 BP1218 BP1219 BP1220 BP1221

stub, precise, dual, handed, leftright, updown, rotate, left-narrow, right-narrow, traditional

Aaron David Fairbanks

BP1214 has the same solution but rotated a quarter-turn clockwise.

Adjacent-numbered pages:
BP1212 BP1213 BP1214 BP1215 BP1216  *  BP1218 BP1219 BP1220 BP1221 BP1222

stub, dual, handed, updown, traditional

Aaron David Fairbanks

https://en.wikipedia.org/wiki/Hex_(board_game)

Adjacent-numbered pages:
BP1240 BP1241 BP1242 BP1243 BP1244  *  BP1246 BP1247 BP1248 BP1249 BP1250

hard, precise, convoluted, dual, rotate, boundingbox, hardsort, challenge, proofsrequired, bordercontent

Aaron David Fairbanks

Adjacent-numbered pages:
BP1249 BP1250 BP1251 BP1252 BP1253  *  BP1255 BP1256 BP1257 BP1258 BP1259

dual, meta (see left/right), links, viceversa

Leo Crabbe

All examples in this Bongard Problem are scatter plots. Each dot represents a data point.

"Positive correlation" means that when the X value increases, the Y value tends to increase as well (in the long run), while "negative correlation" means that when the X value increases, the Y value tends to decrease.

Adjacent-numbered pages:
BP1266 BP1267 BP1268 BP1269 BP1270  *  BP1272 BP1273 BP1274 BP1275 BP1276

Example TM4854 does not fit on either side because when the X value increases, the Y value stays the same.

Example TM4855 does not fit on either side because there is no correlation.

fuzzy, minimal, unwordable, teach, spectrum, dual, handed, leftright, updown, rotate, stable, hardsort, left-narrow, right-narrow

Ben

All examples in this Bongard Problem are solid black shapes.

BP345 is "Intersection of circle and square vs. union of circle and square."

Adjacent-numbered pages:
BP1267 BP1268 BP1269 BP1270 BP1271  *  BP1273 BP1274 BP1275 BP1276 BP1277

EX1 is ambiguous because it might be a small circle minus a large square, or a small square minus a large circle.

easy, nice, precise, dual

Ben