reserve a,b,c for set;

theorem Th14:
  for D being non empty set,f being FinSequence of D st f=<*a,b,c
  *> holds f|2=<*a,b*>
proof
  let D be non empty set,f be FinSequence of D;
  assume
A1: f=<*a,b,c*>;
  f|2 = f|Seg 2 by FINSEQ_1:def 16
    .= <*a,b*> by A1,FINSEQ_6:5;
  hence thesis;
end;
