8 lines regular solution
I'd like to call it an exponential descending cursor



(once) = (start)xxxxxxxx

# locate position between 3 and 4
xxa = ax
xxb = bx
xxc = cx

# delete tail from 4
xa = x
xb = x
xc = x

#delete cursor
(end)x =

On this problem, is there any easier solution? My solution is just brute force xd.
Its like XXXA = XXX (X can be anyletter A, B, C ) for keep first 3 letters. So I wrote all 81(3*3*3*3, 3 = A, B, C) possibilities. So if u guys find easier solution, pls share xd