Updated TODO list.

TODO

 # vim: set fileencoding=utf-8 :
-
- - Fix BisonSyntaxError location tracking.
-
- - Sort polynom by its exponents?
-
- - Fix division by zero caused by "0/0": Catch exception in front-end
-
-smvv@multivac ~/work/trs $ printf "a/0\n??" | ./main.py
-Traceback (most recent call last):
-  File "./main.py", line 75, in <module>
-    main()
-  File "./main.py", line 64, in main
-    node = p.run(debug=args.debug)
-  File "/home/smvv/work/trs/external/pybison/src/python/bison.py", line 258, in run
-    self.report_last_error(filename, e)
-  File "/home/smvv/work/trs/external/pybison/src/python/bison.py", line 251, in run
-    self.engine.runEngine(debug)
-  File "bison_.pyx", line 592, in bison_.ParserEngine.runEngine (build/external/pybison/bison_.c:592)
-  File "/home/smvv/work/trs/src/parser.py", line 195, in hook_handler
-    possibilities = handler(retval)
-  File "/home/smvv/work/trs/src/rules/fractions.py", line 23, in match_constant_division
-    raise ZeroDivisionError('Division by zero: %s.' % node)
-ZeroDivisionError: Division by zero: a / 0.
-
-smvv@multivac ~/work/trs $ printf "0/0\n??" | ./main.py
-Traceback (most recent call last):
-  File "./main.py", line 75, in <module>
-    main()
-  File "./main.py", line 64, in main
-    node = p.run(debug=args.debug)
-  File "/home/smvv/work/trs/external/pybison/src/python/bison.py", line 258, in run
-    self.report_last_error(filename, e)
-  File "/home/smvv/work/trs/external/pybison/src/python/bison.py", line 251, in run
-    self.engine.runEngine(debug)
-  File "bison_.pyx", line 592, in bison_.ParserEngine.runEngine (build/external/pybison/bison_.c:592)
-  File "/home/smvv/work/trs/src/parser.py", line 195, in hook_handler
-    possibilities = handler(retval)
-  File "/home/smvv/work/trs/src/rules/numerics.py", line 73, in match_divide_numerics
-    divide = not divmod(n.value, dv)[1]
-ZeroDivisionError: integer division or modulo by zero
-
  - Last possibilities reduce to a similar result.
 
-smvv@multivac ~/work/trs $ printf "0/1\n??" | ./main.py
-<Possibility root="0 / 1" handler=divide_numerics args=(0, 1)>
-Division of 0 by 1 reduces to 0.
-Division of 0 by 1 reduces to 0.
-
  - ExpressionNode.equals() werkend maken voor alle cases (negatie).
 
- - validation: preorder traversal implementatie vergelijken met andere
-               implementaties.
-
- - No matches for sin(pi), sin(2pi), sin(4pi), etc...
-
  - Create unit tests for node inequivalence operator.
 
  - Line printer: 1 / (n + n)x  ->  1 / (n + n) * x
 
- - Unit tests for strategy.
-
- - Parser: add unit tests for operator associativity (derivatives/integrals).
-
  - Modules:
    + Equations with substitution
-   + Sort
-   + Gonio
+   + Gonio, no matches for sin(pi), sin(2pi), sin(4pi), etc...
 
  - Add parentheses to integral bounds where needed:
    int_(-1)^2 ... dx
    or, fix parser error using the following notation:
    int_-1^2 ... dx
 
- - Base hint selection on the desired final expression.
-   To generate a hint for expression list A, ..., B:
-   1. Create a possibility tree for A.
-   2. Validate all expressions up to B:
-      set ROOT = A
-
-      for each expression C in <A, B] do:
-          if final answer of C is not equal to final answer of A:
-              validation failes at c
-
-          find C in the possibility tree, traversing from ROOT
-
-          if not found:
-              validation continues, but generate an efficiency warning at C
-              # FIXME: validation fails at C?
-
-          set ROOT = C
-    3. Generate a hint:
-      # ROOT should now be equal to B, so lookup of B is unnecessary
-      set N = empty dictionary
-
-      for each possibility of ROOT P node do:
-          evaluate P(B) until the final expression of A is reached
-          set N[P] = the number of explicit possibilities that have been applied in the evaluation
-
-      the hint is that P for which the value of N[P] the smallest
-
- - Optimization: put possibility tree in hashmap: {'expression': [(handler, args, 'applied_expression')], ...}
-   This hashmap can be used to speedup the calculation of possbility trees.
-
 - Fix: int -cf(x) dx (caused infinite loop)
-
-- Idea for validation that is not really working ATM:
-  When validating that a => b:
-  Apply reductions to a to obtain A, this costs N steps.
-  Apply reductions to b to obtain B, this costs M steps.
-  if A != B, validation fails (return status 0)
-  else if M >= N, the uses has done a useless or bad step (return status 1)
-  otherwise (if M < N), the user has reduced the expression correctly (return status 2)
+  Solution: remove baby steps that rewrites f(x) to f(x) ^ 1