Complex sentence: For doing this Ockham was solemnly excommunicated by Pope John XXII, while Ockham believed that John XXII was himself guilty of heresy for refusing to accept the Franciscan claim.
Split into simpler sentences: For doing this Ockham was solemnly excommunicated by Pope John XXII. He believed that John XXII was himself guilty of heresy for refusing to accept the Franciscan claim.