reserve n for Nat;

theorem
  for G be Go-board st len G = width G for j,k,j1,k1 be Nat
st 1 <= j & j <= j1 & j1 <= k1 & k1 <= k & k <= len G holds LSeg(G*(j1,Center G
  ),G*(k1,Center G)) c= LSeg(G*(j,Center G),G*(k,Center G))
proof
  let G be Go-board;
  assume len G = width G;
  then
A1: Center G <= width G by JORDAN1B:13;
  let j,k,j1,k1 be Nat;
  assume that
A2: 1 <= j and
A3: j <= j1 and
A4: j1 <= k1 and
A5: k1 <= k and
A6: k <= len G;
  1 <= Center G by JORDAN1B:11;
  hence thesis by A2,A3,A4,A5,A6,A1,Th6;
end;
