# File lib/HebrewProber.rb, line 181
        def is_non_final(c)
            # The normal Tsadi is not a good Non-Final letter due to words like 
            # 'lechotet' (to chat) containing an apostrophe after the tsadi. This 
            # apostrophe is converted to a space in FilterWithoutEnglishLetters causing 
            # the Non-Final tsadi to appear at an end of a word even though this is not 
            # the case in the original text.
            # The letters Pe and Kaf rarely display a related behavior of not being a 
            # good Non-Final letter. Words like 'Pop', 'Winamp' and 'Mubarak' for 
            # example legally end with a Non-Final Pe or Kaf. However, the benefit of 
            # these letters as Non-Final letters outweighs the damage since these words 
            # are quite rare.
            return [NORMAL_KAF, NORMAL_MEM, NORMAL_NUN, NORMAL_PE].include?(c)
        end