"The standard "foundation" for mathematics starts with sets and their elements. It is possible to start differently, by axiomatising not elements of sets but functions between sets. This can be done by using the language of categories and universal constructions."

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It no longer makes sense to speak of "feeding problems" or "sleep problems" or "negative behavior" is if they were distinct categories, but to speak of "problems of development" and to search for the meaning of feeding and sleep disturbances or behavior disorders in the developmental phase which has produced them.

— Selma Fraiberg