static List<String> PossibleCommands(int lines) {
            List<string> outputList = new List<string>();
            Rec(outputList, lines, "", -1);
            return outputList;
        }

        static void Rec(List<string> outputList, int linesLeft, string stringAcc, int last = -1) {
            // recursion bottom
            if (linesLeft == 0) {
                outputList.Add(stringAcc.Substring(0, stringAcc.Length - 1));
                return;
            }

            // dj, d2j, ...
            for (int i = 1; i < linesLeft; i++) {
                // dNj
                Rec(outputList, linesLeft - i - 1, stringAcc + $"d{i}j ", i + 1);
                if (i == 1) {
                    // dj
                    Rec(outputList, linesLeft - i - 1, stringAcc + "dj ", 2);
                }
            }

            // dd
            Rec(outputList, linesLeft - 1, stringAcc + "dd ", 1);

            // dot command
            if (last > 0 && linesLeft >= last) {
                string add = ". ";
                Rec(outputList, linesLeft - last, stringAcc + add, last);
            }
        }