1. as detailed in section 4 of Bell and Sejnowski (1995)
2. see eqs. 40 and 41 in their paper.
3. Symmetric bimodal densities considered in this paper are sub-Gaussian, however this is not always the case.
4. The presented estimation theory is related to the semiparametrical statistical approach by Amari and Cardoso (1997) and the stability analysis of adaptive blind source separation (Amari et al., 1997a)