reserve n for Nat,
  i,j for Nat,
  r,s,r1,s1,r2,s2,r9,s9 for Real,
  p,q for Point of TOP-REAL 2,
  G for Go-board,
  x,y for set,
  v for Point of Euclid 2;

theorem
  1 <= j & j+1 <= width G implies LSeg(p,1/2*(G*(len G,j)+G*(len G,j+1))
  +|[1,0]|) meets Int cell(G,len G,j)
proof
  assume
A1: 1 <= j & j+1 <= width G;
  now
    take a = 1/2*(G*(len G,j)+G*(len G,j+1))+|[1,0]|;
    thus a in LSeg(p,1/2*(G*(len G,j)+G*(len G,j+1))+|[1,0]|) by RLTOPSP1:68;
    thus a in Int cell(G,len G,j) by A1,Th34;
  end;
  hence thesis by XBOOLE_0:3;
end;
