Coincidentally I had just started speculating about the pedagogical merits of subtraction equivalence classes as an analog to fractions. Nice then to have it la

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).