| 1. | greatest common divisor, least common multiple |
| 2. | relatively prime integers |
| 3. | the Euclidean algorithm |
| 4. | congruence modulo m |
| 5. | Cantor's argument showing that the rational numbers are countable |
| 6. | Cantor's argument showing that the real numbers are uncountable |
| 7. | n! |