Inverse of Multiplicative Inverse

Theorem
Let $\left({F, +, \times}\right)$ be a field whose zero is $0_F$.

Let $a \in F$ such that $a \ne 0_F$.

Let $a^{-1}$ be the multiplicative inverse of $a$.

Then $\left({a^{-1}}\right)^{-1} = a$.

Proof
The multiplicative inverse is, by definition of a field, the inverse element of $a$ in the multiplicative group $\left({F^*, \times}\right)$.

The result then follows from Inverse of Inverse/Group.