Some folks thought they recognised the duel between Granny Weatherwax and Archchancellor Cutangle from T. H. White’s description of a similar duel in his Arthur, The Once and Future King (also depicted as a very funny fragment in Disney’s The Sword in the Stone, which was an animation film based on this book). However, Terry says:
“The magical duel in Equal Rites is certainly not lifted from T. H. White. Beware of secondary sources. Said duel (usually between a man and a woman, and often with nice Freudian touches to the things they turn into) has a much longer history; folkies out there will probably know it as the song ‘The Two Magicians’.”