diff --git a/dlibrary/dlibrary.py b/dlibrary/dlibrary.py
index 012d1dd..3501161 100755
--- a/dlibrary/dlibrary.py
+++ b/dlibrary/dlibrary.py
@@ -88,11 +88,6 @@ IRRELEVANT_PDF_BLOCK_REGEX = re.compile(r'\bTCPDF\b', re.I)
 MULTIPART_RAR_HEAD_REGEX = re.compile(r'^(.+)\.part0*1\.exe$', re.I)
 MULTIPART_RAR_TAIL_REGEX = re.compile(r'^(.+)\.part0*([^1]|[^0].+)\.rar$', re.I)
 
-debug_mode = False
-def debug(s):
-    if debug_mode:
-        print(s)
-
 def open_zipfile_with_encoding(path):
     for enc in ["utf-8", "shift-jis", "shift-jisx0213"]:
         try:
@@ -725,8 +720,6 @@ def unique_hierarchical_prefix_numbering(entries, start_point=0):
     if len(entries) == 1 and not NUMBER_REGEX.search(nname(entries[0])):
         return {None: entries}
 
-    debug(f'Finding unique hierarchical prefix ordering from start point {start_point} for {entries}')
-
     longest_entry = max(entries, key=lambda e: len(nname(e)))
     matches = reversed(list(NUMBER_REGEX.finditer(nname(longest_entry))))
     for m in matches:
@@ -734,7 +727,6 @@ def unique_hierarchical_prefix_numbering(entries, start_point=0):
         if pos < start_point:
             return None
         prefix = nname(longest_entry)[:pos]
-        debug(f'Checking prefix {prefix}')
         if all(nname(e).startswith(prefix) or prefix.startswith(nfc(e.stem)) for e in entries):
             numbering = {}
             for e in entries:
@@ -751,7 +743,6 @@ def unique_hierarchical_prefix_numbering(entries, start_point=0):
             for idx in indices:
                 if len(numbering[idx]) > 1:
                     ents_idx = numbering.pop(idx)
-                    debug(f'Index {idx} has multiple entries')
                     longest = max(ents_idx, key=lambda e: len(nname(e)))
                     next_layer_start = pos + NUMBER_REGEX.match(nname(longest)[pos:]).end()
                     sub_numbering = unique_hierarchical_prefix_numbering(ents_idx, start_point=next_layer_start) or alphabetic_numbering(ents_idx, next_layer_start)
@@ -765,22 +756,22 @@ def unique_hierarchical_prefix_numbering(entries, start_point=0):
     return None
 
 def alphabetic_numbering(entries, start_point):
-    debug(f'Finding alphabetic numbering from start point {start_point} for {entries}')
     alphabetized = {}
     for entry in entries:
         ending = nfc(entry.stem)[start_point:].strip(' -_()')
-        debug(f'{entry} has ending {ending}')
         if len(ending) > 1:
-            debug('Ending is more than one character, giving up')
             return None
         index = 0 if ending == '' else ord(ending.lower()) - ord('a') + 1
         if index < 0 or index > 26:
-            debug('Ending is not a letter, giving up')
             return None
         if (index,) in alphabetized:
-            debug(f'Index value {index} is already present, giving up')
             return None
         alphabetized[(index,)] = [entry]
+    indices = list(alphabetized.keys())
+    indices.sort()
+    for i in range(1, len(indices)):
+        if indices[i][0] - indices[i-1][0] != 1:
+            return None
     return alphabetized
 
 def check_extension(path, exts):
@@ -1137,11 +1128,6 @@ argparser.add_argument(
     default=Path(os.getenv('DLIBRARY_DIR', './dlibrary')),
     help='directory to store dlibrary content and metadata to (default: $DLIBRARY_DIR or ./dlibrary)',
 )
-argparser.add_argument(
-    '-D', '--debug',
-    action='store_true',
-    help='print out debugging info',
-)
 argparser.add_argument(
     '-l', '--locale',
     type=str,
@@ -1291,10 +1277,6 @@ parser_generate.set_defaults(func=generate)
 
 def main():
     args = argparser.parse_args()
-
-    global debug_mode
-    debug_mode = args.debug
-
     args.func(args)
 
 if __name__ == "__main__":