Let $F$ and $G$ be two propositional formula.
Which of the following is/are True?
- $F \vee G$ is a tautology iff at least one of them is a tautology
- if $F \rightarrow G$ is a tautology and $F$ is a tautology, then $G$ is a tautology.
- $(F \rightarrow G) \vee (F \rightarrow \neg G)$ is a tautology.
- $(F \rightarrow G) \wedge (F \rightarrow \neg G)$ is a tautology iff $F$ is a contradiction.