Lemma 1. Suppose triangles ABC and AB′C′ have a common angle at A, and
that the incircle of AB′C′ is not greater than the incircle of ABC. If C′ > C, then
the bisector of C′ is less than the bisector of C.
Proof. Let CF and C′F′ be the bisectors of angles C, C′ of triangles ABC,
AB′C′. Assuming C′ > C, we shall prove that C′F′ < CF.