def union(self, other):
if isinstance(other, tuple):<EOL><INDENT>other = list(other)<EOL><DEDENT>return type(self)(super().__add__(other))<EOL>
Returns a FrozenList with other concatenated to the end of self.

Parameters
----------
other : array-like
    The array-like whose elements we are concatenating.

Returns
-------
diff : FrozenList
    The collection difference between self and other.