theorem
  seq is convergent & (ex k st for n st k<=n holds seq1.n=seq.n) implies
  lim seq=lim seq1
proof
  assume that
A1: seq is convergent and
A2: ex k st for n st k<=n holds seq1.n=seq.n;
  consider k such that
A3: for n st k<=n holds seq1.n=seq.n by A2;
A4: now
    let p;
    assume 0<p;
    then consider n1 such that
A5: for m st n1<=m holds |.(seq.m)-(lim seq).|<p by A1,COMSEQ_2:def 6;
A6: now
      assume
A7:   n1<=k;
      take n=k;
      let m;
      assume
A8:   n<=m;
      then n1<=m by A7,XXREAL_0:2;
      then |.(seq.m)-(lim seq).|<p by A5;
      hence |.(seq1.m)-(lim seq).|<p by A3,A8;
    end;
    now
      assume
A9:   k<=n1;
      take n=n1;
      let m;
      assume
A10:  n<=m;
      then seq1.m=seq.m by A3,A9,XXREAL_0:2;
      hence |.(seq1.m)-(lim seq).|<p by A5,A10;
    end;
    hence ex n st for m st n<=m holds |.seq1.m-(lim seq).|<p by A6;
  end;
  seq1 is convergent by A1,A2,Th19;
  hence thesis by A4,COMSEQ_2:def 6;
end;
