theorem Th49:
  closed_inside_of_rectangle(a,b,c,d) /\ inside_of_rectangle(a,b,c,d)
  = inside_of_rectangle(a,b,c,d)
proof
  set R = closed_inside_of_rectangle(a,b,c,d);
  set P1 = inside_of_rectangle(a,b,c,d);
  thus R /\ P1 c= P1 by XBOOLE_1:17;
  P1 /\ P1 c= P1 /\ R by Th46,XBOOLE_1:26;
  hence thesis;
end;
