Professor Teach is concerned that RB-INSERT-FIXUP might set color [nil [T]] to RED, in which case the

Question:

Professor Teach is concerned that RB-INSERT-FIXUP might set color [nil [T]] to RED, in which case the test in line 1 would not cause the loop to terminate when z is the root. Show that the professor's concern is unfounded by arguing that RB-INSERT-FIXUP never sets color [nil [T]] to RED.