anchor.diff:  <1> Starting from vertex 1, keep taking outgoing edges until a software vertex is reached.
   <2> Starting from vertex 1, and in an infinite loop, emit the vertex if it is a person and then traverser the outgoing edges.
   <3> Starting from vertex 1, keep taking outgoing edges until a vertex is reached that has no more outgoing edges.
  -<4> The same as <3>, but using a predicate argument for `until()`.
  +<4> The same as before, but using a predicate argument for `until()`.
   
   [[retain-step]]
   Retain Step
  
positive.code:                   where(__.as('a').out('knows').as('c')). <1>
                    select('a','c').by('name'); null <2>
  traversal.toString() <3>
  traversal <4>, <5>
  traversal.toString() <6>
  ----
  
  
negative.code: <2> A verification of the type of list returned.
  <3> `fold()` can be provided two arguments --  a seed value and a reduce bi-function ("vadas" is 5 characters + "josh" with 4 characters).
  <4> What is the total age of the people in the graph?
  <5> The same as before, but using a built-in bi-function.
  
  [[group-step]]
  Group Step
  