An introduction to combinatorics concerns mostly counting and probability. As problem-solving ability becomes more advanced, the scope of combinatorics grows, leading students to the intermediate level.
- Counting functions
- Complementary counting
- Constructive counting
- Committee forming
- AoPS Introduction to Counting & Probability Book
- Ritvik Rustagi's ACE The AMC 10 and AMC 12 book has a chapter on combinatorics.