theorem Th16:
  for f1 being FinSequence holds mid(f1,0,0)=f1|1
proof
  let f1 be FinSequence;
  0-1<0;
  then
A1: 0-'1=0 by XREAL_0:def 2;
  0-'0+1=0-0+1 by XREAL_1:233
    .=1;
  then mid(f1,0,0)=(f1/^(0-'1))|1 by Def3;
  hence thesis by A1;
end;
