|    In the paradox of the twins, we can talk about
| three frames: The frame of the twin who remains at
| rest (we called it Twin A's frame), the outgoing
| frame of Twin B, who moves away, and the incoming or
| returning frame of Twin B.

Nope.
Twins A and B have but one frame each.
Changing direction does NOT change the frame at all.
The x-coordinate does NOT change.
The frame does NOT cease to inertial.
Arguing acceleration is  stepping outside SR
and is cheating.

However, SR is BS.
So is LET.
[remainder snipped unread, the premise is false]
Androcles.