[r-t] Plain Bob leadheads

[Fred Bone]

On 19 February 2021 at 9:14, Mark Davies said:

> Please can someone produce, or point me at, a concise proof of this lemma:
> 
> PB1: In a palindromic treble-dominated method with Plain Bob leadheads, on
> an even number of bells, the lead end place notations must be 12 or 1n.

What is the definition of "palindromic"? Does it necessarily exclude the 
use of jump changes?