"Internal repetition of action has been a staple of Shakespearian dramatic structure since the early 1950s, the double wooing of Katherine and Bianca in The Taming of the Shrew being perhaps the most illustrative case," (McDonald 104).
Though McDonald's point has never been brought to my attention before, I can definitely see the duplicity in Shakespeare's dramatic structure exhibited in a number of his other plays. A Midsummer Night's Dream has Puck influencing the love affairs of both the humans wandering the forest and the fairy queen. There are the twins of the same name in A Comedy of Errors. In Romeo and Juliet there are the two feuding families, two lovers, and two agents (Friar Laurence and the Nurse) aiding Romeo and Juliet on their tryst. Also, two key characters die, one from each familial affiliation, Mercutio (Montague) and Tybalt (Capulet). I am sure there is much more to be said on this duplicity gimmick Shakespeare has seemed to utilize in his dramatic structures; however, these were just a few examples I came up with off the top of my head. They were easy to pick out, once I came to an understanding with McDonald's theory.