Part I

1. Draw the expression tree for $((\neg(a))\Rightarrow (b)) \Leftrightarrow ((a)\vee (b))$
2. Write down the formula represented by the expression tree:
3. Prove that $\neg(\neg((\neg(a))\vee (b)))$ is a propositional formula.
4. Why is $(a)\neg(b)$ not a propositional formula?
5. Why is $(\wedge)\vee(a)$ not a propositional formula?
6. Is $x_1$ a propositional formula? Justify!

Part II

1. Draw the expression tree for $a \Rightarrow b \Rightarrow c$. Note: you might want to put in the parentheses first!
2. Draw the expression tree for $a \Rightarrow b \wedge c \Rightarrow d$. Note: you might want to put in the parentheses first!
3. Draw the expression tree for $\neg a \Rightarrow b \Leftrightarrow a \vee b$
4. Write down the formula represented by the expression tree below without any unnecessary ( )s: