How to concatenate lists/arrays?

Question

YAML

I'm trying to figure out how to combine the contents of multiple lists. Example:

A = ['a']
B = ['b']
C = A + B
C >> ['a', 'b']

Tried several solutions like this one:

A: &A
  - 'a'
B: &B
  - 'b'
C:
  *A
  *B

But nothing happened.