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

theorem Lem10:
  x =*=> y & y ==> z implies x =*=> z
  proof
    assume
A1: x =*=> y;
    assume
A2: y ==> z;
A4: y =*=> z by A2,Th2;
    thus x =*=> z by A1,A4,Th3;
  end;
