On 03/30/16 at 02:44pm, Marko Rauhamaa wrote: > Jussi Piitulainen <jussi.piitulai...@helsinki.fi>: > > > Manolo Martínez writes: > >> On 03/30/16 at 01:40pm, Jussi Piitulainen wrote: > >>> Yes, and most many-to-one mappings are *not* surjective. > >> > >> Well, I don't know about most, there are uncountably many surjective > >> and non-surjective many-to-one mappings :) > > > > Ok, safer to say that some many-to-one mappings are not surjective. > > > > I was thinking of finite sets, and not even really thinking. But even > > with infinite domain and infinite codomain, there can be uncountably > > many mappings without any of them being a surjection - just have the > > codomain be a larger infinity. > > I don't even know if you can say much about the cardinality (or > countability) of mappings. The general set of mappings can't exist. The > *class* of mappings does exist in some set theories, but I don't believe > classes have cardinality. >
I guess I was thinking of the cardinality of the set of tuples with members of the domain in the first member and their image in the second. Many of those sets will have a well defined cardinality (unless I'm missing something, which is entirely possible). Anyway, this is all terribly OT. Thanks for humoring me. Manolo -- https://mail.python.org/mailman/listinfo/python-list
