Paare und Tripel halbkonzentrischer Kreise der euklidischen Ebene

In [1], semi-concentric circles have been defined and considered, also their special nets and pencils.—The isochordal curve and the isogonal curve of two circles, the isochordal lines and the isogonal points of three circles show many differences according to whether the two or three circles are semiconcentric or not. Results for semi-concentric circles are developed here, while results for other circles have been given in [2] and [5].