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Re: [xmca] a minus times a plus

Andy Blunden wrote on the "math social-construction" thread:-
> On a side note, a lot of people calling on various metaphors
> to justify -x-=+ have never addressed the question a kid
> might ask as to why the example given doesn't prove that a -
> when **added* to a - gives a +. I certainly had kids
> confront me with that one. It is very easy to skate over the
> hidden equation of multiplication with intersection and
> compounding and so on which to a lot of non-mathematicians
> looks much more like addition. The link between these
> operations is obviously NOT arbitrary, is it? But nor is it
> obvious,
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