Hi Jonas, > I just realized that my example was maybe a bad one. But imagine the > same example for a space where the base ring _does_ coerce into the > space. A base-changed base ring would then not coerce, so the pushout > construction would be used and it would return the wrong space, > resp. my arguments would make more sense there, no?
Do you mean something like the following? Assume you have a construction EvenSubspace() that applies to spaces of polynomials and returns the subspace of all polynomials that only have even powers of x. This of course includes constants. Suppose you have a ring homomorphism A -> B and you want to do pushout(B, EvenSubspace(PolynomialRing(A, 'x'))) I guess my approach would indeed eliminate the application of EvenSubspace() because it doesn't know that B still coerces into EvenSubspace(PolynomialRing(B, 'x')). If this is the case, the criterion for eliminating a "coercion-reversed" construction step F probably needs to be made more strict: if both of the original objects still coerce into the result of applying F, then we do want to apply F. Does that sound reasonable? Peter -- You received this message because you are subscribed to the Google Groups "sage-devel" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-devel+unsubscr...@googlegroups.com. To post to this group, send email to sage-devel@googlegroups.com. Visit this group at http://groups.google.com/group/sage-devel. For more options, visit https://groups.google.com/d/optout.
