Re: A discussion of 'Tachyons, the 4-momentum ...'

In DOI: 10.13189/ujpa.2023.170101, Figure 4 depicts a thought
experiment involving FTL communication.  This figure is
attached to this post.  We, the viewers, are at rest with
observers A and B.
 At event E1, observer A, at x = 0, t = vL/c^2, sends an
infinitely-fast tachyon signal to observer B, who receives
it at x = L, t = vL/c^2.  B immediately passes it to D, who