Defining the momentum space annihilation operator ${ }^3$
$$
\boldsymbol{\phi}(\mathbf{p})=\int\langle\mathbf{p} \mid \mathbf{r}\rangle \boldsymbol{\psi}(\mathbf{r}) d^3 r
$$
derive the commutation (or anticommutation) relations for $\boldsymbol{\phi}(\mathbf{p})$ and $\boldsymbol{\phi}^{\dagger}(\mathbf{p})$. For the Bose-Einstein case, show that the mixed commutator of field operators in coordinate and momentum space is
$$
\left[\boldsymbol{\phi}(\mathbf{p}), \boldsymbol{\psi}^{\dagger}(\mathbf{r})\right]=\langle\mathbf{p} \mid \mathbf{r}\rangle
$$