Note on [27-28]: originally 2 PdB. modified by Drewry to SkCh. O. Otto says best variant is corners in PdB, 1c in SkCh
Note: on  the original says »RH«, but »BH« is widely used.
Note: Cosh explicitly tells 1c to pass Lsh in [9-24]; however the Rsh pass is quite common, and nicknamed »Mairi's Divorce«.