Construct unambiguous context-free grammars for each of the following languages. In each case show that your grammar is correct.
- Arithmetic expressions in postfix notation.
- Left-associative lists of identifiers separated by commas.
- Right-associative lists of identifiers separated by commas.
- Arithmetic expressions of integers and identifiers with the four binary operators $+, -, *, /$.
- Add unary plus and minus to the arithmetic operators of $(d)$.
