public List<DispLine> sequential() throws Exception {
        List<DispLine> disps = new ArrayList<>();
        int nlIndex = 0;        // index of start of next line
        int disp = 0;           // byte displacement of current line
        int lineNumber = 0;
        while(true) {
            char currentChar;
            StringBuilder sb = new StringBuilder();
            while ((currentChar = (char)br.read()) != (char)-1 && currentChar != '\n') {
                sb.append(currentChar);
                nlIndex++;
            }
            if (currentChar ==(char)-1) {
                break;
            } else {
                String line = sb.toString();
                if (patt.matcher(line).find())
                    disps.add(new DispLine(disp, line));
                final int currentLineLength = nlIndex - disp + 1;
                disp += currentLineLength;
                nlIndex = disp;
            }
            lineNumber++;
            if (lineNumber % 1_000_000 == 0) System.out.println(lineNumber);
        }
        return disps;
    }