Omitting Types Theorem Logic Closure Properties of Computable Sets Discrete Mathematics Herbrand's Theorem for First-Order Validity Logic Representability of Primitive Recursive Functions in Peano Arithmetic Logic Basic Closure and Characterisation Discrete Mathematics Ryll-Nardzewski Theorem Logic Relative Szemerédi Theorem Combinatorics Hypersimple Sets Are Simple Logic Discrete Mathematics Area Combinatorics Subarea