Nested list comprehension with two lists

Question

I understand how the simple list comprehension works eg.:

[x*2 for x in range(5)] # returns [0,2,4,6,8]

and also I understand how the nested

Answer 1

this sequence

res = [x + y for x in l2 for y in l1 ]

is equivalent to

res =[]
for x in l2:
    for y in l1:
        res.append(x+y)