theorem Th44:
  x in dom Macro i iff x= 0 or x= 1
proof
  set si=Macro i, A = NAT;
A1: card si = 2 by Th40;
  hereby
    assume
A2: x in dom si;
    reconsider l=x as Element of NAT by A2;
    reconsider n = l as Element of NAT;
    n < 1+1 by A1,A2,AFINSQ_1:66;
    then n <= 1 by NAT_1:13;
    hence x= 0 or x= 1 by NAT_1:25;
  end;
  thus thesis by A1,AFINSQ_1:66;
end;
