
A minus times a minus is a plus - ColinWright
http://robjlow.blogspot.com/2017/10/a-minus-times-minus-is-plus.html
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jonsen
Coincidentally I had just started speculating about the pedagogical merits of
subtraction equivalence classes as an analog to fractions. Nice then to have
it laid out by a mathematician.

I think school algebra could benefit from a more analog view on addition-
subtraction versus multiplication-division. The similarities are obscured by
the difference in notation (and of course by too much rote-ruling).

