If A⊆B then for any set C, prove that (C−B)⊆(C−A)
Let A⊆B be given.
Let xϵ(C−B). Then,
xϵ(C−B)⇒xϵC and x/ϵB
⇒xϵC and x/ϵA [∵A⊆B]
∴ (C−B)⊆(C−A)
Hence, A⊆B⇒(C−B)⊆(C−A)
If A, B, C are three sets such that A⊂B, then prove that C−B⊂C−A