Short proof: All the elements in B are also in A.
Long proof:
.
I disagree, this is standard notation - even year 8 students should be aware of the notation of to represent the universal set, to represent the number of elements in set A, and that . Even if they are infinite, the same logic holds if you were to draw a Venn Diagram of the situation.
Ha ha ha ... you jest
Cardinality? That is not the notation I know.to represent the number of elements in set A,
Let your be the unit disk, let A be some disk contained in , now what does your notation mean?and that . Even if they are infinite, the same logic holds if you were to draw a Venn Diagram of the situation.
CB