theorem Th36:
  G*(1,1)-|[1,1]| in Int cell(G,0,0)
proof
  set s1 = G*(1,1)`2, r1 = G*(1,1)`1;
  G*(1,1) = |[r1,s1]| by EUCLID:53;
  then
A1: G*(1,1)-|[1,1]| = |[r1-1,s1-1]| by EUCLID:62;
  s1 < G*(1,1)`2+1 by XREAL_1:29;
  then
A2: s1-1 < G*(1,1)`2 by XREAL_1:19;
  r1 < G*(1,1)`1+1 by XREAL_1:29;
  then
A3: r1-1 < G*(1,1)`1 by XREAL_1:19;
  Int cell(G,0,0) = { |[r,s]| : r < G*(1,1)`1 & s < G*(1,1)`2 } by Th18;
  hence thesis by A1,A2,A3;
end;
