Transitive inference, class inclusion and a variety of other inferential abilities have strikingly similar developmental profiles—all are acquired around the age of five…. [Our research] results point to a fundamental cognitive principle under development during childhood that is the capacity to compute (co)products in the categorical sense.
Ingest that, if you will, and then listen to Tom Lehrer’s song “New Math”, which was written in the early 1960s.
BONUS: Watch Tom perform a slightly later variation of the song, written to explain to the British public how simple it would be for them to convert to decimal currency.