reserve X for ARS, a,b,c,u,v,w,x,y,z for Element of X;
reserve i,j,k for Element of ARS_01;

theorem ThA1:
  for s being set holds s is Element of ARS_01 iff s = 0 or s = 1
  proof
    let s be set;
    the carrier of ARS_01 = {0,1} by Def18;
    hence thesis by TARSKI:def 2;
  end;
