Robust CYK-Parse (on CNF strings) with easy CYK-Parse-Tree Retrieval. Based on algorithm described by Ernest Davis.

1. This program is written using python3.5.
2. The input files used within the main python file, cyk_parser.py, are necessary and must be in its directory.
3. get_grammar.py is imported by cyk_parser.py and is used to read the grammar from file (grammar.txt), parse the grammar text and create the necessary objects. in which the grammar is stored.
4. To run, simply pass the file as an argument to the python interpreter python3.5 cyk_parser.py.