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;
