Presence and absence of signals inside a reaction are inherent to
  the synchronous paradigm, as well as clocks which are sets of
  instants that indicate when a given condition is fulfilled over a
  sequence of reactions (e.g. when a signal is present). Clocks are
  essential to capture the control in data-flow specifications; more
  generally relations between clocks should be analyzed to detect
  e.g.\ inconsistencies and verify some properties. These relations
  express particular safety properties many of which can be verified
  without considering the dynamic of systems, by means of a static
  abstraction. We propose a language CL to describe such
  properties and prove it decidable. Finally, model-checking is
  derived for e.g. Signal programs, on the basis of a translation
  from the static abstraction of Signal into CL.