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* API changes
* 40 and 50 Expression.subs() now takes 'default' thanks to kronuz
* 45 simplify=False is now the default for parse and related functions or methods.
* 40 Use "&" and "|" as default operators
* Bug fixes
* 60 Fix bug for "a or b c" which is not a valid expression
* 58 Fix math formula display in docs
* Improve handling of parse errors