Strings can be manipulated in a complicated way and produce the same result. All the four statements below produce the same result.
m, n: N;
Reverse((Prt_btwn (m, n, α)) = Prt_btwn (| α | - n, | α | - m, Reverse(α));
Prt_btwn (m, n, Reverse(α)) = Reverse(Prt_btwn (| α | - n, | α | - m, α));
Example:
α = <4, 7, 3, 6 > ; | α | = 4;
m = 1; n = 3;
| α | - m = 3; | α | - n = 1;
Reverse ((Prt_btwn (1, 3, α)) = Reverse (< 7, 3>) = <3, 7>;
Prt_btwn (| α | - n, | α | - m, Reverse(α)) = Prt_btwn (1, 3, <6, 3, 7, 4>) =
<3, 7>;
Prt_btwn (m, n, Reverse(α))=Prt_btwn (1, 3, <6, 3, 7, 4>) = <3, 7>;
Reverse(Prt_btwn (| α | - n, | α | - m, α )) = Reverse(Prt_btwn(1, 3, α)) =
Reverse(<7, 3>) = <3, 7>.
