Let $\text{P}$ be a compound proposition over $4$ propositional variables $: a,b,c,d.$
We know that for $a$ compound proposition over $n$ propositional variables, we have $2^{n}$ rows in the truth table.
Every row of the truth table of $\text{P}$ is called an “Interpretation” of $\text{P}.$
A row in the truth table of $\text{P}$ is called “model” iff $\text{P}$ is true for that row.
Let $\text{P}$ be “ $a \leftrightarrow b$”
How many models are there for $\text{P}?$