Question

Prove: If C⊂A and D⊂B then D−A⊂B−C

Answer 1

Let
`x\in D\setminus A`, so that
`x\in D` but
`x\\ot\in A`. Since
`D\subset B`, it follows that
`x\in B`, and since
`C\subset A`, it follows that
`x\\ot\in C`, which means
`x\in B\setminus C`.