let G be Group; :: thesis: for F being FinSequence of the carrier of G holds F |^ ((len F) |-> (@ 1)) = F
let F be FinSequence of the carrier of G; :: thesis: F |^ ((len F) |-> (@ 1)) = F
defpred S₁[ FinSequence of the carrier of G] means $1 |^ ((len $1) |-> (@ 1)) = $1;
A1: for F being FinSequence of the carrier of G
for a being Element of G st S₁[F] holds
S₁[F ^ <*a*>]

proof

let F be FinSequence of the carrier of G; :: thesis: for a being Element of G st S₁[F] holds
S₁[F ^ <*a*>]
let a be Element of G; :: thesis: ( S₁[F] implies S₁[F ^ <*a*>] )
set A = F ^ <*a*>;
assume A2: S₁[F] ; :: thesis: S₁[F ^ <*a*>]
A3: len <*a*> = 1 by FINSEQ_1:40;
A4: ( len <*(@ 1)*> = 1 & len ((len F) |-> (@ 1)) = len F ) by CARD_1:def 7;
len (F ^ <*a*>) = (len F) + (len <*a*>) by FINSEQ_1:22;
hence (F ^ <*a*>) |^ ((len (F ^ <*a*>)) |-> (@ 1)) = (F ^ <*a*>) |^ (((len F) |-> (@ 1)) ^ <*(@ 1)*>) by A3, FINSEQ_2:60
.= (F |^ ((len F) |-> (@ 1))) ^ (<*a*> |^ <*(@ 1)*>) by A3, A4, Th19
.= F ^ <*(a |^ 1)*> by A2, Th22
.= F ^ <*a*> by GROUP_1:26 ;
:: thesis: verum

end;

A5: S₁[ <*> the carrier of G]

proof

set A = <*> the carrier of G;
thus (<*> the carrier of G) |^ ((len (<*> the carrier of G)) |-> (@ 1)) = (<*> the carrier of G) |^ (0 |-> (@ 1))
.= (<*> the carrier of G) |^ (<*> INT)
.= <*> the carrier of G by Th21 ; :: thesis: verum

end;

for F being FinSequence of the carrier of G holds S₁[F] from FINSEQ_2:sch 2(A5, A1);
hence F |^ ((len F) |-> (@ 1)) = F ; :: thesis: verum