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;
reserve l,m,n for Element of ARS_02;
reserve A for set;

theorem LemN7:
  x is_normform_of y & z =*=> y implies x is_normform_of z by Th3;
