The main theorem is as follows: If circle DEF touches on its inside two points F and G on two circles EGH and FGH, whose diameters added together equal the diameter of the largest circle DEF, and if chord EF is drawn between the contact points E and F, it will pass through the point G, the intersection of the two smaller circles, and also the sum of arcs EG and FG will be equal to the arc EF.
Original Source Citation
Acta Academiae Scientiarum Imperialis Petropolitanae, Volume 1781: I, pp. 249-258.
Opera Omnia Citation
Series 1, Volume 26, pp.249-257.