David Benson on 2002-02-08 wrote: Early on, John Gray and others noticed that functors ought not compose on-the-nose, but up-to-isomorphism, and (I believe) called the result <<pseudo-functors>>. Well, there is nothing <<pseudo>> about it and it is these latter entities that deserve the name <<functor>>, with the first 50 years of use then becoming XXX functor where XXX might be <<young>> or <<nasal>> or ... The issues here seem to be: What are the possible comparison methods for composition, identity, etc., how shall they be briefly named, and which shall be the default? The most conventional answers to these questions seem to be: . COMPARISON | SYSTEMS | USAGE EXAMPLES . | [E] [I] [M] | [E] [I] [M] . ___________ | ______ ______ ______ | ________ ________ ________ . equality | ------ strict strict | X strict X strict X . isomorphism | pseudo ------ strong | pseudo-X X strong X . morphism | lax lax ------ | lax X lax X X The leftmost column gives the three most common comparison methods. (morphism actually has two variants depending on the sense of the morphism.) Next come three different naming systems for the three comparison methods. [E], [I] and [M] designate both a system and a reference for it: [E] Kelly and Street, Review of the Elements of 2-Categories (1974), Section 1.5 [I] Blackwell, Kelly and Power, Two-Dimensional Monad Theory (1989), Section 1.2 [M] same reference as [E]; each reference provides examples, historical justification, and comparisons to alternative conventions (e.g., in the setting of bicategories, homomorphism for strong morphism). In each naming system the default comparison method has a '------' (the lack of a name) as its "name". Finally, in the USAGE EXAMPLES, for X take functor or morphism or (natural) transformation or algebra or .... The original quotation suggested taking up-to-isomorphism as the norm; that would seem to put it squarely in the [I] camp, making its XXX = <<strict>>. It would be interesting to expand the table to take into account other comparison methods and systems; also it would be in some ways be simpler if the isomorphism comparison could be denoted by a single term, but pseudo and strong have the advantage of clearly indicating where they stand relative to the norms in their respective systems. It has been stated that the notion of pseudo-functor originated with Grothendieck's study of fibrations (fibred categories) in the 1961 SGA Cat\'egories fibr\'ees et descente; perhaps Madame Ehreshmann or Monsieur Benabou might care to expand, confirm or comment on that... Keith 19-Feb-2002 11:36:18 -0400,2670;000000000001-00000000