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Wrong explanation in chap 2, section 3.2.1.1 Relating Orderings #5

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@fraterenz

Thank you very much for making this book available, it's very interesting and very well written.

I spotted a mistake (I think?) in the explanation in the relating orderings chapter.
I think for the pushforward orderings we need f to be bijective, but the reason is simply that we need to map each input to the output space, otherwise orderings won't be defined in Y.

So this is correct I think: "If f is not also surjective, and hence bijective, then we cannot pushforward orderings on the input space to orderings on the output space." But the explanation is wrong (see snippet):

orderings on the output space. The problem is that if any pair
of output elements are associated with multiple input elements,
\begin{align*}
y_{1} &= f(x_1) = f(x_1')
\\
y_{2} &= f(x_2) = f(x_2'),
\end{align*}
then we can have conflicting input orderings,
\begin{align*}
x_1 &< x_2
\\
x_2' &< x_1',
\end{align*}
that cannot be combined into a consistent output ordering.

Does it make sense? Thanks!

Francesco

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