The wavefunction is $\Psi(\mathbf{r}_1, \sigma_1, \mathbf{r}_2, \sigma_2, \ldots, \mathbf{r}_{100}, \sigma_{100})$ — a function of 300 spatial coordinates and 100 spin indices. - The wavefunction must be antisymmetric under exchange of any two electrons: $\Psi(\ldots, \mathbf{r}_i, \ldots, \mathbf{r