reserve a,b,c for set;

theorem
  for D being non empty set,f,CR being File of D holds f
  is_preposition_of addcr(f,CR)
proof
  let D be non empty set,f,CR be File of D;
  addcr(f,CR)=ovlcon(f,CR) by FINSEQ_8:def 11
    .=f^(CR/^(len ovlpart(f,CR))) by FINSEQ_8:def 3;
  hence thesis by Th24;
end;
