Suggestion: make sequence and map interfaces more similar

[Jussi Piitulainen]

Manolo Martínez writes:

> On 03/30/16 at 01:40pm, Jussi Piitulainen wrote:
>> Manolo Martínez writes:
>  >
>> > I think it's with your definition of surjection. Bijections are
>> > surjective, no?
>> 
>> 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.

It depends on the types. Which makes the concept not easily applicable
to Python data structures as such.