let recherche a m = let ml = String.length a and al = String.length a and i = ref 0 and j = ref 0 in
  while !i < al-ml-1 do
    begin
      while (!j<ml) && (m.[ !j] = a.[ !i]) do
        begin
          i := !i+1;
          j := !j +1

        end
      done;
      if !j = ml then
        i := al-ml +1
      else
        begin
          i := !i - !j+1;
          j:=0
        end
    end
  done;
  !j = ml;;