Let $\alpha, \beta$ be two propositional formulas.
Which of the following assertions is true?
- $\alpha$ is valid if and only if True $\models \alpha $.
- For any $\alpha$, False $\models \alpha$.
- $\alpha \models \beta $ if and only if the sentence $(\alpha \Rightarrow \beta$ is valid.
- $\alpha \equiv \beta$ if and only if the sentence $(\alpha \Leftrightarrow \beta)$is valid.
