Wednesday April 2

First we proved that there are no natural numbers between 0 and 1, hence only one integer strictly between -1 and 1.
This is handy later; it says that the only multiple of d strictly between -d and d is 0.
Then we proved the "division algorithm":
given an integer n and a natural d>0, there exist unique integers p,r with r in [0,d) such that n=pd+r.
Then we introduced the "divides" notation a|b, and proved a couple of easy things about it. More to come.