Lemma A.1Subsets of **N** are countable

Proposition A.2Subsets of countable sets are countable

Corollary A.3More rules for countable sets

Proposition A.4Unions of countalbe sets are countable

Lemma A.5Sequences of 0's and 1's are uncountable

Proposition A.6Open intervals of **R** are uncountable

Corollary A.7Existence of irrationals