(x|y)=(\sum_{i=1}^{n}\alpha_i e_i|\sum_{i=1}^{n}\beta_i e_i) = \sum_{i=1}^{n}\sum_{j=1}^{n}(\alpha_i e_i|\beta_j e_j) = \sum_{i=1}^{n}\alpha_i \overline{\beta_i}