7 Apr
1990
7 Apr
'90
4:30 p.m.
I replied much too quickly to the Charles Wells question. What is correct is that any functor that preserves all finite weak limits preserves all finite limits. For an example of an endofunctor on SETS that fails to preserve weak pullbacks consider the functor that takes the empty set to the empty set and everything else to a one-element set. For a counterexample to my hasty response consider the covariant power- set functor (using direct images); it preserves weak pullbacks but not pullbacks. Peter Freyd