Something

function MiStrPos(a,b: string): boolean;
var I: integer;
begin
  Result:=false;
  if ((Length(a) > 0) and (Length(b) > 0)) then begin
    for I:=1 to Length(a)-Length(b)+1 do begin
      if Copy(a,I,Length(b)) = b then begin
        Result := True;
        exit;
      end;
    end;
  end;
end;