Mike wrote: << Is there a geometric way to understand the Taylor series for sin and cos? The closest I've been able to find is a combinatorical explanation (below), but it doesn't seem to help much.
I'd love to know such a way to understand their Taylor series. I recently gave a talk to a bunch of smart youngsters about complex numbers, and was unable to find a truly graceful way to explain why exp(ix) = cos(x) + i sin(x), (without deriving their Taylor series). So if anyone knows a way to see this, I'd love to know it. But of course that would require giving exp a meaning on the imaginaries. Mike continued: << The paper "Objects of Categories as Complex Numbers" by Marcelo Fiore and Tom Leinster and says that under certain conditions, objects can behave as though they had complex cardinalities. It turns out that data types of typed programming languages satisfy the conditions; the data structure T = T^2 + T + 1 of trees with 2 (ordered), 1, or 0 children, behaves like "i". It is not the case that T^4 is isomorphic to the one-element set, but T^5 = T. Since it's a countably infinite set, this may seem obvious, but there's a way of constructing the isomorphism using only distributivity and the defining isomorphism above, so the cardinality is also preserved. . . . . . .
I don't really understand this, but it sounds fascinating. --Dan ________________________________________________________________________________________ "Outside of a dog, a book is man's best friend. Inside of a dog, it's too dark to read." --Groucho Marx