[isabelle] more beginner questions

1) Is there a datatype for characters in isabelle?  I would like
   to prove stuff about a real world grammar for a language of

2) This is really basic but giving me a headache.  How can I make
   an optional tuple?  I tried "('a, 'a) option"  but that didnt seem
   to work properly.

3) Do any isabelle users hang out on some real-time chat network where
   a beginner like me could pester them?  For example irc.freenode.net
   #isabelle would be nice.  *hint* *hint*
   I'm there, but I'm afraid I'm in no position to answer questions :)

thanks in advance.

Tim Newsham

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