# Hajnal, Andras

## Unions of triangle free graphs ★★★

**Problem**Does there exist a graph with no subgraph isomorphic to which cannot be expressed as a union of triangle free graphs?

Keywords: forbidden subgraph; infinite graph; triangle free

## The Erdös-Hajnal Conjecture ★★★

**Conjecture**For every fixed graph , there exists a constant , so that every graph without an induced subgraph isomorphic to contains either a clique or an independent set of size .

Keywords: induced subgraph