let f, g be FinSequence of (TOP-REAL 2); for p being Point of (TOP-REAL 2) st f . (len f) = g . 1 & p in L~ g & f is being_S-Seq & g is being_S-Seq & (L~ f) /\ (L~ g) = {(g . 1)} & p <> g . 1 holds
(mid (f,1,((len f) -' 1))) ^ (R_Cut (g,p)) is being_S-Seq
let p be Point of (TOP-REAL 2); ( f . (len f) = g . 1 & p in L~ g & f is being_S-Seq & g is being_S-Seq & (L~ f) /\ (L~ g) = {(g . 1)} & p <> g . 1 implies (mid (f,1,((len f) -' 1))) ^ (R_Cut (g,p)) is being_S-Seq )
assume that
A1:
f . (len f) = g . 1
and
A2:
p in L~ g
and
A3:
f is being_S-Seq
and
A4:
g is being_S-Seq
and
A5:
(L~ f) /\ (L~ g) = {(g . 1)}
and
A6:
p <> g . 1
; (mid (f,1,((len f) -' 1))) ^ (R_Cut (g,p)) is being_S-Seq
(mid (f,1,((len f) -' 1))) ^ (R_Cut (g,p)) is_S-Seq_joining f /. 1,p
by A1, A2, A3, A4, A5, A6, Th47;
hence
(mid (f,1,((len f) -' 1))) ^ (R_Cut (g,p)) is being_S-Seq
; verum