code: public Set<PhysicalEntity> getNonUbiques(Set<PhysicalEntity> entities, RelType ctx)
  	{
  		Collection<SmallMolecule> ubiques = getUbiques(entities, ctx);
  		if (ubiques.isEmpty()) return entities;
  
  		Set<PhysicalEntity> result = new HashSet<PhysicalEntity>(entities);
  		result.removeAll(ubiques);
  		return result;
  	}
docs: Gets the non-ubiquitous physical entities in the given set and in the given context. It is
  assumed that the given set is either left or right of a Conversion. If there is no
  non-ubiquitous element in the set, then the least ubique(s) are added to the result.
  @param entities left or right of a conversion
  @param ctx are these entities input or output
  @return non-ubiquitous physical entities in the given context