Winter 2004 QG Seminar Errata

John Baez

• On page 4 of week 1 it should say, at the very end, "or S = emptyset".
• On page 19 of week 2 the guess after "huh?!" doesn't completely make sense, since F is the Fibonacci structure type, we have an isomorphism between F and 1 + FZ + FZ², not FZ + FZ².
• On page 19 of week 2 the isomorphism should read "G + GZ³ is isomorphic to 1 + GZ + GZ²".
• On page 20 of week 2 there is, not exactly an error, but certainly an infelicity: we are mainly using "S" to stand for an arbitrary set, but also using it in the expression "SV" to stand for the symmetric algebra on a vector space V.
• On page 36 of week 4 the equation "P(4) = 4" should read "P(4) = 5" - this is an example of Ramanujan's theorem that P(5m+4) is congruent to 0 mod 5.
• On page 43 of week 5 where it says "regular Borel measures" it should read "finite regular Borel measures".
• On page 26 of week 5 the categories FinSet and CTherm should be underlined. Recall that we underline a category to refer to its "decategorification", that is, the set of isomorphism classes of its objects. If we decategorify the 2-rigs FinSet and CTherm we get rigs, and the obvious functor from FinSet to CTherm gives a homomorphism from the first rig to the second.

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