todo

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0. Convert general exceptions in ah.py to specialized exceptions
1. Test {} {} {}
2. Get each exception to trigger once
3. 

xxxx 1. check whether a given gla symbol is defined more than once
xxxx 2. you can't redefine a gla symbol in the con
xxxx 3. you can't redefine a color
xxxx 4. you can't color a literal that doesn't exist
xxxx 4a. you can't use a symbol on the RHS of a CON rule unless it's defined.
5. you can't color a literal in a rule that doesn't include that literal
6. you can't use an integer that's out-of-bounds
   - this implies you have to count the terminals of a symbol?
   - this also implies you have to count the occurrences of a symbol
   - we could store the elements of the consymbol as a computed tree on the symbol's entity.
7. You can't color anything that's recursive. 

Add mapping for predefined colors
Need to be able to parse multiple values for the color attributes