The planar Ramsey number PR(C4,K7)

The planar Ramsey number PR(H1,H2) is the smallest integer n such that any planar graph on n vertices contains a copy of H1 or its complement contains a copy of H2. It is known that the Ramsey number R(C4,K7)=22. The planar Ramsey numbers PR(C4,Kl) for l≤6 are known. In this paper we show that PR(C4,K7)=20.