When linguists study an old and dead language, they usually try guessing the meaning of a word based on the context in which the word occurs. By comparing the different contexts a word is used in, they can usually easily deduce the meaning of a word. Sometimes however, they come across words that are only used once in all texts known in that language. Such words usually can't be translated, because the context in which these words occur are barely known.

A word that occurs only once in the texts of a certain language, is called a hapax legomenon. This term is a transliteration of the Greek ἅπαξ λεγόμενον. The literal translation is 'what is said once'. The term is not only used for words that occur once in a certain language. For example, it is also used for words that only occur once in an entire oeuvre of a certain author, or in a certain text.

Assignment

Write a function hapax that takes a string as an obligatory argument and prints a list as a result. This list must contain the hapax legomena from the given text, sorted in alphabetical order. To determine whether a word is a hapax legomenon, we consider the variants of words that consist solely of lowercase letters. We consider a word in a text as the longest possible succession of letters from the alphabet.

Example

>>> kapper = '''Kapper Knap, de knappe kapper,
... knipt en kapt heel knap, maar de knecht van
... kapper Knap, de knappe kapper, knipt en kapt
... nog knapper dan kapper Knap, de knappe kapper, 
... knipt en kapt'''
>>> hapax(kapper)
['dan', 'heel', 'knapper', 'knecht', 'maar', 'nog', 'van']
>>> betty = '''Betty Botter bought a bit of butter.
... The butter Betty Botter bought was a bit bitter
... And made her batter bitter.
... But a bit of better butter makes better batter.
... So Betty Botter bought a bit of better butter
... Making Betty Botter's bitter batter better'''
>>> hapax(betty)
['and', 'but', 'her', 'made', 'makes', 'making', 's', 'so', 'the', 'was']