Part 2

Introducing Prt_Btwn() - the Substring function

Prt_Btwn () (pronounced as "part between") retrieves a substring located between the two specified positions of the original string:

Prt_Btwn (afterPsn, lastPsn, whichString);

The substring does not include the element at the position afterPsn, and will include the element at the lastPsn. The position of the first element of the mathematical string is 1, not zero, as in the programming language arrays.

Example:
α = <7, 9, 4, 1, 3 >;
Prt_Btwn (1, 4, α ) = <9, 4, 1 >;

In this example 7 is at position 1, 9 is at 2, etc. We remove a substring after the position 1 starting with integer 9 and up to, and including position 4. The resulting substring is <9, 4, 1 >.

If we want the substring to include the first element of the original string, we will use 0 as the starting position:

Prt_Btwn (0, 2, <3, 4, 5>) = <3, 4 >;