A -. B            NB. items in A but not in B
┌──────┐
│Serena│
└──────┘
   A -.~ B           NB. items in B but not in A
┌───┐
│Jim│
└───┘
   A                 NB. A is a sequence without duplicates
┌────┬──────┬───┬────┐
│John│Serena│Bob│Mary│
└────┴──────┴───┴────┘