**Input:** Two qubits (stored in an array of length 2) in an arbitrary two-qubit state ${\color{blue}\alpha} \ket{00} + {\color{blue}\beta} \ket{01} + \gamma \ket{10} + \delta \ket{11}$.

**Goal:**  Change the two-qubit state to ${\color{red}\beta} \ket{00} + {\color{red}\alpha} \ket{01} + \gamma \ket{10} + \delta \ket{11}$.

> This task can be solved using one library function; as an exercise, try to express the solution using several (possibly controlled) Pauli gates.  