combinatorics
branch of discrete mathematics
diamond principle
combinatorial principle that there exists a family of sets 𝐴(𝛼)⊆𝛼 for 𝛼<ω₁ such that for any 𝐴⊆ω₁, the set of 𝛼’s with 𝐴∩𝛼=𝐴(𝛼) is stationary in ω₁
combinatorial design
symmetric arrangement of finite sets
discrete geometry
branch of geometry that studies combinatorial properties and constructive methods of discrete geometric objects