Show that in the power set P(A) = ( set of all subset of A ), the relation of 'contained in defined as A1 R A2 if A1 is a subset of A2, is a partial order relation.

Show that in the power set P(A) = ( set of all subset of A ), the relation of 'contained in defined as A1 R A2 if A1 is a subset of A2, is a partial order relation.