Show that the following problems are not recursively enumerable:
- The set of pairs $(M,w)$ such that $TM \ M$, started with input $w$, does not halt.
- The set of pairs $(M_{1},M_{2})$ such that $L(M_{1}\cap L_(M_{2})=\phi$.
- The set of triples $(M_{1},M_{2},M_{3})$ such that $L(M_{1}) = L(M_{2})L(M_{3})$ ; i.e., the language of the first is the concatenation of the languages of the two $TM's$.
