135. Countability

135.1. Countable and Uncoutable Sets

1. Countable (Discrete)

One-to-one correspondence with positive integers

E.g.,

• Positive integers
• Integers
• Pairs, triples, quadruples, … of positive integers
• rational numbers , with

2. Uncountable (Continuous)

• Intervals ()
• Reals
• Plane