  This document is the aggregation of six discussions of Lopes et al. (2010)
that we submitted to the proceedings of the Ninth Valencia Meeting, held in
Benidorm, Spain, on June 3-8, 2010, in conjunction with Hedibert Lopes' talk at
this meeting, and of a further discussion of the rejoinder by Lopes et al.
(2010). The main point in those discussions is the potential for degeneracy in
the particle learning methodology, related with the exponential forgetting of
the past simulations. We illustrate in particular the resulting difficulties in
the case of mixtures.
