Given two sets:
$a = \{1,2,3\} $
$b=\{1,2,3\}$
Are they supersets of each other? Are they subsets of each other?
Given two sets:
$a = \{1,2,3\} $
$b=\{1,2,3\}$
Are they supersets of each other? Are they subsets of each other?
What is the definition of subset? Of superset? It shouldn't be difficult to prove that a set is a subset and superset of itself. Actually, two sets $A$ and $B$ are identical if and only if $A$ is both a subset and superset of $B$.
As others have pointed out, it is a quite trivial consequence of the definition of the notion of a subset that if $a = b$ then $a \subset b$ and $b \subset a$.
But also do note that it is a bit unhappy to say 'given two sets' here when you've given two different labels to one and the same set!