trello = ["a", "b", "c"]
jira = ["d", "c", "e"]
# - is the difference
# & is the intersection
# | is the union
trello - jira # ["a", "b"] -> a and b exist in trello but not jira
trello & jira # ["c"] -> c exists in both trello and jira
trello | jira # ["a", "b", "c", "d", "e"] -> both arrays have been joined