function RightStr(const AStr: String; Len: Integer): String;
begin
end;
 
function LeftStr(const AText: string; const ACount: Integer): string;
begin
end;
 
 
function izraz (s1: string): string;
  var s2 : string;
      t,s: array[1..30] of char;
      j: integer;
      factor,potency,posx,pos_pot: integer;
      polinom: array[0..10] of integer;
 
begin
repeat
   posx := pos('x',s2);                  //find x
 
    if posx > 1 then                       // if we find x, then read characters before x
    begin
      j:=1;
      repeat
        t[j] := s2[j];
        j:=j+1;
      until ( s2[j] = 'x' ) ;
      factor := strtoint(t);
    end
    else                               // if x is on the first place, then factor is 1
    begin
      if posx = 1 then
        factor := 1
      else
      begin
        // t := niz1;
        s2 := '';
        factor := strtoint(t);
      end;
    end;
 
    if posx >= 1 then                          // if x is found, search ^
    begin
      pos_pot := pos('^',s2);
      if pos_pot > 1 then
        begin
           s2 := rightstr(s2,length(s2)-pos_pot);
           j:=1;
           repeat
            s[j] := s2[j];
            j:=j+1;
          until ( s2[j] = '+' ) or ( s2[j] = '-' ) or ( j>length(s2) ) ;
          potency := strtoint(s);
          s2 := rightstr(s2,length(s2)-j+1);
        end
      else
      begin
        potency := 1;
        s2 := rightstr(s2,length(s2)-posx);
      end;
    end
    else
    potency := 0;
    polinom[potency] := factor;
 until s2 = '';
end;
 
 
function integral(input: string): extended;
var p,i, t2 : integer;
    niz1: string;
    l: integer;
    lower_limit, upper_limit: string[2];
 
begin
      delete(input,1,9);
      delete(input,length(input),1);
      p:=pos(',',input);
      niz1:=copy(input,1,p-1);
      izraz(niz1);
      l:=length(input);
      t2:=l-2;
  begin
      if input[l-3]='-' then
        upper_limit:=copy(input,length(input[i-3]),2);
      if input[i-6]='-' then
       lower_limit:=copy(input,length(input[i-6]),2)
       else
       lower_limit:=inttostr(l-5);
 
      if input[l-3]<>'-' then
      upper_limit:=inttostr(l-2);
      if input[l-5]='-' then
       lower_limit:=copy(input,length(input[i-5]),2)
       else
       lower_limit:=inttostr(l-4);
  end;
end;

function integral(input: string): extended;//WAITS STRING ,BACK EXTENDED
var p,//STORES THE ',' POSITION IN THE *INPUT* STRING
    i, t2 : integer;
    niz1: string;
    l: integer;
    lower_limit, upper_limit: string[2];
 
begin
      {
procedure Delete(var S: String; Index: Integer; Count:Integer);
Delete deletes Count characters from S starting at the Indexth position. If Index is larger than the length of S, no characters are deleted. If Count specifies more characters than remain starting at the Indexth position, the remainder of the string is deleted.
      }
      delete(input,1,9);//DELETE(INPUT,from 1ST,9 CHARS)
      delete(input,length(input),1);//DELETE(INPUT,length of input,1 char)
{AFTER THE TWO DELETE PROCEDURE THE *INPUT*'S VALUE IS EMPTY!!!!!}
      p:=pos(',',input);//HOW CAN IT FIND IN A EMPTY STRING????
{
SO WHEN I TRY TO USE YOUR FUNCTION THIS IS NOT WORKING AT ALL,AND WHERE IS THE BACK VALUE
Integral:=?????? this is important part of a function....
What do you want? Integrate a function to another?
We need 'back value' to integrate them... 
 
}