         var commonPrefix = 0
         for i in 0..<min(chars.count, previousChars.count) {
             if chars[i] != previousChars[i] { break }
-            commonPrefix++
+            commonPrefix += 1
         }
         
         // Minimize nodes before continuing.

                while char != newLine
                {
                    buffer.append(char)
                    i++
                    if i >= characters.count { break }
                    char = characters[i]
                }
                dawg.insert(buffer)
                buffer.removeAll()
                i++
            } while i != characters.count
            dawg.minimize(0)
            dawg.save(outputPath)

            wordLength: wordLength, prefix: [DawgLetter](), filled: filled,
            filledCount: filled.count, source: rootNode,
            blankLetter: String(blankLetter).utf8.first!, results: &results)
        return results.count > 0 ? results : nil
    }
}