Thats not a list. Its a way of saying that you want the byte in that pointer. Lets ues the alphabet as an example for this.
ABCDEF
is in pointer K
If you use {K+3}
You get
D
Why? If this was not a group of letters but lets say a string it get the third byte in the string.
Ok now thats covered. You could have a "matrix" but it would really just be like a list.
TI-OS syntax for lists and matrix use "," between element. You have to use bytes.
Example:
Matrix:
[4,8,3]
[2,4,7]
Is really just
(4 8 3 2 4 7)->P
And to get the element you need just use {P+#}
Smarter people please correct if needed!
Hope this helps!