code: public boolean isSubspace(Subspace subspace) {
      return this.dimensionality <= subspace.dimensionality && //
          BitsUtil.intersectionSize(dimensions, subspace.dimensions) == dimensionality;
    }
docs: Returns true if this subspace is a subspace of the specified subspace, i.e.
  if the set of dimensions building this subspace are contained in the set of
  dimensions building the specified subspace.
  
  @param subspace the subspace to test
  @return true if this subspace is a subspace of the specified subspace,
  false otherwise