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I’m trying to understand what you’re attempting. Do you mean to start with this:
List A
aaa
bbb
ccc

List B
xxx
yyy
zzz

Output:
List C
aaaxxx
bbbyyy
ccczzz

If so, keep in mind that “aaa,bbb,ccc” is not a list, but a single text item. So maybe change it so that the inputs are not a list?