Right examples are called "derangements".
Adjacent-numbered pages: BP926 BP927 BP928 BP929 BP930  *  BP932 BP933 BP934 BP935 BP936
handed, leftright, sequence, traditional, left-listable, right-listable
dot_clusters_sequence_horizontal [smaller | same | bigger]
Aaron David Fairbanks
Attributes are shading, shape, and number.
There are always three groups.
This problem is related to the card game Set.
Adjacent-numbered pages: BP1133 BP1134 BP1135 BP1136 BP1137  *  BP1139 BP1140 BP1141 BP1142 BP1143
nice, notso
William B Holland
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, traditional
Based on BP91, which is the same, except for that the right side is "four identical elements".
Adjacent-numbered pages: BP1221 BP1222 BP1223 BP1224 BP1225  *  BP1227 BP1228 BP1229 BP1230 BP1231
stub, arbitrary, number, traditional