[1][2] The question of how to explain the similarities among the Gospels Matthew, Mark, and Luke is known as the synoptic problem.
According to the four-document hypothesis, the author combined Mark, the Q source, and L to produce his gospel.
[1] I. Howard Marshall (1994) stated: "Luke rightly regarded these sources as reliable".
[3] James R. Edwards (2009) equated the L source with the Hebrew Gospel referred to by patristic authors.
[8] Theissen (1998) went further, stating that the special material comprises nearly half of the Gospel of Luke.