Today I read a paper titled “Context-free multilanguages”
The abstract is:
This article is a sketch of ideas that were once intended to appear in the author’s famous series, “The Art of Computer Programming”.
He generalizes the notion of a context-free language from a set to a multiset of words over an alphabet.
The idea is to keep track of the number of ways to parse a string.
For example, “fruit flies like a banana” can famously be parsed in two ways; analogous examples in the setting of programming languages may yet be important in the future.