code: public SPFPerson lookup(String identifier) {
  		boolean isReachable = mSearchInterface.lookup(identifier);
  		if (isReachable) {
  			return new SPFPerson(identifier);
  		} else {
  			return null;
  		}
  	}
docs: Allows to retrieve a reference to a remote person given its identifier.
  This reference is valid until the given person is reachable from the
  proximity middleware.
  
  @param identifier
  @return