Построить множество символов, встречающихся в строке ровно 2 раза

var s, c: string;
    t: char;
    i: byte;
    m, n: set of char;
begin
  writeln('Enter string:');
  readln(s);
  m := [];
  n := [];
  for i := 1 to length(s) do
    if s[i] in n
      then exclude(m, s[i])
      else if s[i] in m
        then include(n, s[i])
        else include(m, s[i]);
  writeln('Set of the symbols which are found in string exactly on two times:');
  c := '';
  write('[');
  for i := 0 to 255 do
    begin
      t := char(i);
      if (t in m) and (t in n)
        then begin
          write(c);
          if length(c) = 0 then c := ', ';
          write(t)
        end
    end;
  write(']');
  readln
end.

  for t:=#0 to #255 do
    if (t in m) and (t in n) then begin

  writeln('Set of the symbols which are found in string exactly on two times:');
  if m * n = []
    then write('Empty set')
    else for t := #0 to #255 do
      if (t in m) and (t in n)
        then write(t, ' ');
  readln
end.

var
  m:set of char;
  c:array[char] of byte;
  i:integer;
  s:string;
begin
  write('Enter string>');
  readln(s);
  m:=[];
  for i:=1 to length(s) do begin
    inc(c[s[i]]);
    if c[s[i]]=2 then Include(m,s[i]) else if c[s[i]]>2 then Exclude(m,s[i]);
  end;
  write('Set:[');
  for i:=0 to 255 do
    if chr(i) in m then write(#32+chr(i));
  writeln(']');
end.

for cc in m do write(cc);

сс:char;