decidable intersect undecidable Hello I'm kind of having trouble with computability, so my question is
I need to define af language A and B such that A is decidable and B is undecidable 
when I do $A\cap B $ is decidable.
also oppositely i need to define a language A which is decidable and B i undecidable where $A\cap B$ is undecidable.
If someone could give me some examples it would be very a preciated thanks:)

Just let $B$ be any undecidable language and $A$ either the empty language or the language containing all strings from the underlying alphabet.
