Having for the moment run out of steam as far as geometric algebra is concerned, I thought I might for a while resume banging my head against an ancient brick wall. It hasn't taken me long to stub my toe (or to mix my metaphors). Upon earnestly scanning the following introductory documents, http://en.wikipedia.org/wiki/Category_theory http://plato.stanford.edu/entries/category-theory/ http://math.ucr.edu/home/baez/rosetta.pdf each equipped with apparently impeccable credentials, I find that none of them can agree about whether the objects of a category belong to a set (Stanford), a class (Wikipedia), a "collection" (Baez & Stay), or an "aggregate" (anon --- mislaid this one). Furthermore, they are similarly contradictory (and in one case confused) about whether the morphisms thereof comprise a set or a class. I'm not going to insist that authors commit to some particular flavour of set theory, appreciating that category theory may well provide it with an alternative foundation. However, I feel entitled to expect that --- after nearly half a century --- the pedagogy of this discipline might have managed to reach agreement concerning fundamental definitions! Would anybody care to cast some light on this disturbing inconsistency? Fred Lunnon