If one expression is equivalent to a second expression, and the second

expression is equivalent to a third expression, then the first expression is

equivalent to the third expression. $($This is called "transitivity" of equivalence.$)$

Explain in words why the expressions $"P=>Q"$ and $"$ not$(not{Q}^{{?}^{?}}P)"$ are equivalent,

without using truth$-$tables: Use De Morgan's law, transitivity, and equivalences

that were proved in previous questions.