Function union

pattern/graph/__init__.py:975–976

(a, b)

# a & b => elements that appear in a as well as in b.
# a - b => elements that appear in a but not in b.
def union(a, b):
    return list(set(a) | set(b))
def intersection(a, b):
    return list(set(a) & set(b))
def difference(a, b):