theorem
  1 <= i & i <= len G & 1 <= j & j <= width G implies G*(i,j) in LSeg(G*
  (1,j),G*(len G,j))
proof
  assume that
A1: 1 <= i & i <= len G and
A2: 1 <= j & j <= width G;
A3: G*(i,j)`1 <= G* (len G,j)`1 by A1,A2,SPRECT_3:13;
  1 <= len G by A1,XXREAL_0:2;
  then
A4: G*(1,j)`2 = G*(len G,j)`2 by A2,GOBOARD5:1;
  G*(1,j)`2 = G*(i,j)`2 & G*(1,j)`1 <= G*(i,j)`1 by A1,A2,GOBOARD5:1
,SPRECT_3:13;
  hence thesis by A4,A3,GOBOARD7:8;
end;
