This paper reconsiders refinements which introduce actions on the concrete
level which were not present at the abstract level. It draws a distinction
between concrete actions which are "perspicuous" at the abstract level, and
changes of granularity of actions between different levels of abstraction.
The main contribution of this paper is in exploring the relation between
these different methods of "action refinement", and the basic refinement
relation that is used. In particular, it shows how the "refining skip" method
is incompatible with failures-based refinement relations, and consequently some
decisions in designing Event-B refinement are entangled.Comment: In Proceedings Refine 2011, arXiv:1106.348
