A Countable and Uncountable Sets the natural numbers n=(1, 2, 3, .. are countable Definition a set s is countable if it is finite. or it is infinite and there is a bijection f:N→SCountable and Uncountable Sets ◼ the natural numbers N = {1,2,3,…} are countable ◼ Definition: a set S is countable if it is finite, or it is infinite and there is a bijection f: N → S