reserve i,n,m,k,x for Nat,
  i1,i2 for Integer;

theorem Th5:
  0 in 0-SD_Sub_S
proof
  reconsider ZERO = 0 as Integer;
  0 > 0 - 1;
  then 0 -' 1 = 0 by XREAL_0:def 2;
  then
A1: Radix(0-'1) = 1 by POWER:24;
  ZERO is Element of INT by INT_1:def 2;
  hence thesis by A1;
end;
