Exercise L

Consider the following principle:

Suppose $\mathcal{A}$ and $\mathcal{B}$ are logically equivalent. Suppose an argument contains $\mathcal{A}$ (either as a premise, or as the conclusion). The validity of the argument would be unaffected, if we replaced $\mathcal{A}$ with $\mathcal{B}$.

Is this principle correct? Explain your answer.