theorem Th33:
  for G being Matrix of TOP-REAL 2 holds cell(G,i,j) is closed
proof
  let G be Matrix of TOP-REAL 2;
A1: v_strip(G,i) is closed by Th17;
  cell(G,i,j)=h_strip(G,j) /\ v_strip(G,i) & h_strip(G,j) is closed by Th16,
GOBOARD5:def 3;
  hence thesis by A1,TOPS_1:8;
end;
