Unsatisfiable (k,(4*2^k/k))-CNF formulas
  A boolean formula in a conjuctive normal form is called a (k,s)-formula if every clause contains exactly k variables and every variable occurs in at most s clauses. We prove the existence of a (k, 4 * (2^k/k))-CNF formula which is unsatisfiable. 
Heidi Gebauer