Originally Posted by

**PvtBillPilgrim** How can I prove the following:

if the cardinality of A1 = the cardinality of A2, the cardinality of B1 = the cardinality of B2, B1 is a subset of A1, and B2 is a subset of A2,

then the cardinality of (A1 / B1) = the cardinality of (A2 / B2) where / is the set difference operation

I know there exists a bijective function f: A1 to A2 and a bijective function g: B1 to B2. I need to find a bijective function h: (A1 / B1) to (A2 / B2). Can someone fill in the details?

Thanks for your help.