  Give deterministic necessary and sufficient conditions to guarantee that if a
subspace fits certain partially observed data from a union of subspaces, it is
because such data really lies in a subspace.
  Furthermore, Give deterministic necessary and sufficient conditions to
guarantee that if a subspace fits certain partially observed data, such
subspace is unique.
  Do this by characterizing when and only when a set of incomplete vectors
behaves as a single but complete one.
