reserve a,b,c for set;

theorem Th21:
  for D being non empty set,r being FinSequence of D holds ovlpart
  (<*>D,r)=<*>D & ovlpart(r,<*>D)=<*>D
proof
  let D be non empty set,r be FinSequence of D;
  <*>D^r=r & r^<*>D=r by FINSEQ_1:34;
  hence thesis by FINSEQ_8:14;
end;
