reserve i1 for Element of INT;
reserve j1,j2,j3 for Integer;
reserve p,s,k,n for Nat;
reserve x,y,xp,yp for set;
reserve G for Group;
reserve a,b for Element of G;
reserve F for FinSequence of G;
reserve I for FinSequence of INT;

theorem Th13:
  1_INT.Group = 0
proof
  reconsider e = 0 as Element of INT.Group by INT_1:def 2;
  for h being Element of INT.Group holds h * e = h & e * h = h;
  hence thesis by GROUP_1:4;
end;
