Note: [3-4] is NOT in DTr position.
3C Chain Progression was earlier known as Chaperoned Chain Progression
(1c continues into the new reel, on second turn 1c casts to 4pl and 3c (in 2pl) dances on into the new reel)
Unofficial: On 2nd turn, 4c has an easier start if 1c+3c+4c dance a 3c Poussette
After their second turn, 1c casts to 4pl on  as 4c steps up
Note: Cosh explicitly tells 1c to pass Lsh in [9-24]; however the Rsh pass is quite common, and nicknamed »Mairi's Divorce«.