def sol_tracker(w2v_model, solution):
    """Keep a record of those solution words that do not appear in the W2V vocabulary

    Args :
      w2v_model : standard Word2Vec 'KeyedVectors' data structure
      solution  : List of tokenised words representing solution

    """

    sol_errors = []
    for word in solution:
        # Must account for words not in W2V's vocabulary (e.g. 'to')
        try:
            _ = w2v_model[word]
        except KeyError:
            sol_errors.append(word)
            continue

    return sol_errors