The sources of the Gospel of John

Many believe that the Gospel of John went through two or three stages, or editions, before reaching its current form around 90–110 CE.  The scholarly consensus in the second half of the 20th century was that John was independent of the synoptic gospels (Matthew, Mark, and Luke).  However, there are now many who believe that John knew some version of Mark and possibly Luke, as he shared some vocabulary and clusters of incidents arranged in the same order with these Synoptics.  This Gospel of John made extensive use of the Jewish Scriptures, as John quoted from them directly.  He referenced important figures from the Hebrew Scriptures and used narratives from them as the basis for several of Jesus’ discourses.  However, this biblical author felt free to write independently.  Many incidents in John, do not have parallels in the Synoptics.  Many scholars believe he drew these from an independent source called the “signs gospel.”  The speeches of Jesus could come from a second “discourse source.”  Most people agree that the prologue to John was an early Christian hymn.  The Logos of this prologue derived from both the Jewish concept of Lady Wisdom and from the Greek philosophers.  What do you know about the sources of the Gospel of John?