> Hi:
>
> What is the reason for having the ordered pair defined as
>
> [x, y] = { { x,y }, { x } };
>
> and not as
>
> [x, y] = { x, {x, y} }
I think the other one would not prove: [x,y]=[u,v]=>x=y&y=u without
regularity axiom.
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