code: function altPair(first, second) {
    first.out.accepting = false;
    second.out.accepting = true;
  
    first.out.addTransition(EPSILON, second.in);
  
    return new NFA(first.in, second.out);
  }
docs: ----------------------------------------------------------------------------- Alteration NFA fragment: `abc` 
  Creates a connection between two NFA fragments on epsilon transition.
  
  [in-a] --a--> [out-a] --ε--> [in-b] --b--> [out-b]