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 Lem26:
  X is WN UN* & x =*=> y implies nf x = nf y
  proof
    assume
A1: X is WN UN*;
    assume
A2: x =*=> y;
A4: nf y is_normform_of x by A2,A1,Lem22,LemN7;
    thus nf x = nf y by A1,A4,Lem23;
  end;
