code: public Mappings uniqueAtoms() {
          // we need the unique predicate to be reset for each new iterator -
          // otherwise multiple iterations are always filtered (seen before)
          return new Mappings(query, target, new Iterable<int[]>() {
  
              @Override
              public Iterator<int[]> iterator() {
                  return Iterators.filter(iterable.iterator(), new UniqueAtomMatches());
              }
          });
      }
docs: Filter the mappings for those which cover a unique set of atoms in the
  target. The unique atom mappings are a subset of the unique bond
  matches.
  
  @return fluent-api instance
  @see #uniqueBonds()