These are a few…
The set {0,1}
The set {-1, +1}
The Successor Function
Proof by Induction
Going from 10 inches to 25.4 centimeters. Yes, this is really simple, but working with units becomes very helpful when doing physics problems and later on there are things in math which it first don’t make any sense at all until you suddenly realize, hey, this is something we do when we make a jump from inches to centimeters.
Rob Sterling 