However, little more was known until the early 1990s, when several authors began to make connections between the approximation of maximum cliques and probabilistically checkable proofs, and used these connections to prove hardness of approximation results for the maximum clique problem.
Little more was known until the early 1990s. This was however. Several authors began to make connections between the approximation of maximum cliques. Several authors began to make connections between probabilistically checkable proofs. Several authors used these connections. This was to prove hardness of approximation results for the maximum clique problem.