 
       test.deepEqual ['a'], graph.parentless()
       test.deepEqual ['b'], graph.childless()
+
+      test.deepEqual ['a'], graph.parents('b')
+      test.deepEqual [], graph.parents('a')
+
+      test.deepEqual ['b'], graph.children('a')
+      test.deepEqual [], graph.children('b')
 
       test.deepEqual [], graph.whereAllParentsIn []
       test.deepEqual [], graph.whereAllParentsIn new Set()


      test.ok new Set(12, 13, 14, 11, 15).equals graph.childless()

      test.ok new Set().equals graph.whereAllParentsIn []
      test.ok new Set(2).equals graph.whereAllParentsIn [1]
      test.ok new Set(6, 8).equals graph.whereAllParentsIn [5, 3]

        [0, 7]
        [0, 10]
        [0, 13]
        [0, 14]
        [1, 2]
        [1, 9]
        [1, 13]
