Is Father Alive? Rav Tells Rabbi Chiya
Rav arrives from Bavel and Rabbi Chiya asks after his parents; Rav's evasive answers tell him, without a lie, that his brother and sister have died.
Rabbi Chiya’s father had a son, Aivu, from a previous marriage of his. Rabbi Chiya’s mother had a daughter, Ima, from a previous marriage of hers. Aivu and Ima, who were unrelated (step-brother and stepsister), married and had a child and named him Rav. In other words, Rav was the son of Rabbi Chiya’s half-brother and half-sister. (If this sounds complicated, wait until we reach Maseches Yevamos!)
The following incident (told here as explained by Rashi) is mentioned in the Gemara (Mo’ed Kattan 20a): Rav traveled from Babylonia to Eretz Yisrael. Upon his arrival, Rabbi Chiya, his uncle, met him and asked him, “Is father alive?”—meaning, “Is your father (my brother, Aivu) alive?”
Rav replied, “Is mother alive?”— meaning, “Is my mother alive? Why do you ask about my father (your brother) and not my mother (your sister, Ima)?”