Strings are likely the object in question whenever you are dealing with “text,” “characters,” “patterns,” or “labels.”

Learning to think recursively is learning to look for big things that are made from smaller things of exactly the same type as the big thing.

Recursive descriptions of objects require both decomposition rules and

Permutations are likely the object in question whenever your problem seeks an “arrangement,” “tour,” “ordering,” or “sequence.”

Order does not matter in subsets

Points are likely the object in question whenever your problems work on “sites,” “positions,” “data records,” or “locations.”

Trees are likely the object in question whenever your problem seeks a “hierarchy,” “dominance relationship,” “ancestor/descendant relationship,” or “taxonomy.”

Polygons and polyhedra are likely the object in question whenever you are working on “shapes,” “regions,” “configurations,” or “boundaries.”

Subsets are likely the object in question whenever your problem seeks a “cluster,” “collection,” “committee,” “group,” “packaging,” or “selection.”