[FOM] Replacement
Andrej Bauer
Andrej.Bauer at fmf.uni-lj.si
Wed Aug 15 05:26:14 EDT 2007
Isn't replacement required for construction of initial algebras (and
final coalgebras) of functors? For example, given a functor F:Set->Set,
one often considers the colimit of the diagram
0 --> F0 --> F(F0) --> F(F(F0)) --> ...
The colimit is constructed as a quotient of the disjoint sum of the
family {0, F0, F(F0), F(F(F0)), ...}. But how do we form this family if
not by replacement?
This is certainly "ordinary math" as such constructions are used in
topology, algebra and theoretical computer science, at least.
Andrej Bauer
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