rational numbers as ratio of two integers.
(etymology: rational/reason/ratio, cf. french)

NO DECIMALS! NO CALCULATORS!
(exception: n+1/2 or n+1/10, it's sometimes okay: 17.5 is pretty clear)

discs, compliments of discs, punctured discs,
also talk about 2D, 3D, etc. (mention n-dimentional space) and do the distance
formula.
note that a 1D punctured disc has two sides, but a 2D punctured disc is
connected (related to Anindya's proof of fundamental theorem of calculus).

note that there's a lot more directions in 2D and higher, and that this
clarifies some of the subtleties we note in 1D calculus.

1.6...