Fix bug in citekey generation.

papers/repo.py

@@ -84,12 +84,12 @@ class Repository(object):
         year = article.fields['year']
         prefix = '{}{}'.format(first_author.last()[0][:6], year[2:])
 
-        letter = 0, False
+        letter = 0
         citekey = None
 
         citekey = prefix
         while citekey in self.citekeys and citekey not in allowed:
-            citekey = prefix + alphabet[letter[0]]
+            citekey = prefix + alphabet[letter]
             letter += 1
 
         return citekey
@@ -97,4 +97,4 @@ class Repository(object):
     def create_number(self):
         count = int(self.papers_config['count'])
         self.papers_config['count'] = count + 1
-        return count
+        return count