Quasar Lenses and Galactic Streams: Outlier Selection and GAIA Multiplet
  Detection
  I describe two novel techniques originally devised to select strongly lensed
quasar candidates in wide-field surveys. The first relies on outlier selection
in optical and mid-infrared magnitude space; the second combines mid-infrared
colour selection with GAIA spatial resolution, to identify multiplets of
objects with quasar-like colours. Both methods have already been applied
successfully to the SDSS, ATLAS and DES footprints: besides recovering known
lenses from previous searches, they have led to new discoveries, including
quadruply lensed quasars, which are rare within the rare-object class of quasar
lenses. As a serendipitous by-product, at least four candidate Galactic streams
in the South have been identified among foreground contaminants. There is
considerable scope for tailoring the WISE-GAIA multiplet search to stellar-like
objects, instead of quasar-like, and to automatically detect Galactic streams.
