The distribution of relative proper motions of wide binaries in GAIA
  DR2: MOND or multiplicity?
  We examine the distribution of on-sky relative velocities for wide binaries
previously assembled from GAIA DR2 data and focus on the origin of the high
velocity tail of apparently unbound systems which may be interpreted as
evidence for non-Newtonian gravity in the weak field limit. We argue that this
tail is instead explicable in terms of a population of hidden triples, i.e.
cases where one of the components of the wide binary is itself a close binary
unresolved in the GAIA data. In this case the motion of the photocentre of the
inner pair relative to its barycentre affects the apparent relative proper
motion of the wide pair and can make pairs that are in fact bound appear to be
unbound. We show that the general shape of the observed distributions can be
reproduced using simple observationally motivated assumptions about the
population of hidden triples.
