Filtering 2 lists of numbers

Question
1

I have 2 lists of numbers:

List A - 5, 10, 15, 20
List B - 1, 2, 3, 6, 21

I want to filter list A such that it contains only the numbers where the number + 1 is in List B.
Using the example above, the filtered list would be 5, 20.

I don’t want to do this with looping, just straight filtering. Can’t seem to figure it out because the math operators aren’t available in the expressions where I need them to be. Anyone?

2

If interested, I’m available to talk through your problem live (am currently hosting free office hours - see here ). In any case, have you tried:

Create a new list List C where every item is the numbers in List B minus 1 . Then find the intersection of List A with List C

3

Yes, that would totally work, but how do you create the new list where every item is the numbers in List B minus 1?