Part 6
Properties of the Part_btwn()

3. Concatenation of the leading part of the string with the trailing part of the string produces the original string.

n : Ν; then
Prt_btwn (0, n, α) o Prt_btwn (n, | α |, α) = α;

Example:
n = 2;
α = <2, 4, 6, 8, 10>; | α | = 5; then
Prt_btwn (0, 2, α) = <2, 4> and Prt_btwn (2, 5, α) = <6, 8, 10>;
Prt_btwn (0, 2, α) o Prt_btwn (2, 5, α) = <2, 4, 6, 8, 10>
which is the original string.