Removing useless production from CFG

In order to make it simple, I do not care lambda productions and unit productions.

Let G = (V, T, S, P) be CFG, where V = {S, A, B, C} and T = {a, b}. (You can change these variables and symbols) Take production rules from user input and print production rules after removing useless productions.

Language

python3

Usage

Run remove_useless_prodrule.py

python3 remove_useless_prodrule.py

First input : number of production rules

Example:

Input production rules of the CFG G = (V, T, S, P) where V = {S, A, B, C} and T = {a, b}
1. Input the number of production rule : 6

Second input : production rule of the form 'A -> ab'

Example:

2. Input the production rules of the form 'A -> ab'
1) S -> aS
2) S -> A
3) S -> C
4) A -> a
5) B -> aa
6) C -> aCb

Print production rules before/after removing useless production rules

Before elminating useless production : 
S -> aS
S -> A
S -> C
A -> a
B -> aa
C -> aCb
---------------------------------------
After elminating useless production : 
S -> aS
S -> A
A -> a