HP 39gs Master Manual page 192

SIZE(<list>) or SIZE(<matrix>)
This function returns the size of the list or matrix specified. Since normal
users would probably know anyway, and could find out easily via the list
catalog, this is clearly another of those functions which are of more use
to programmers (who won't know when they write their program just
how long the list you will ask it to deal with will be when you eventually
run the program). If the object is a matrix then the return value is a two
element list as {rows, columns}.
Σ
LIST(<list>)
This function returns the sum of all the elements of a list.
Eg. would return a value of 10.
LIST({2,3,5})
REVERSE(<list>)
This function reverses the order of elements in a list.
Eg. would return {10,7,1,4,2}
REVERSE({2,4,1,7,10})
SORT({list})
This function returns a list that is sorted into ascending order.
If you want the list in descending order instead then
use .
REVERSE(SORT({list}))
See page 137 for an example of using to assign rank orders to a list of values.
SORT
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