Where $K = \{x | φ_x(x) \downarrow\}$, $φ_x$ is a $\mu$-recursive function computing $M_x$, $M_x$ is Turing machine with Godel's number $x$. Set $A$ is "1-reducible" to set $B$ ($A \leq_1 B$) when there exists invertible function $f = (\forall x \in N)[x \in A \Longleftrightarrow f(x) \in B]$.
I need that for part of my homework. Thank you for your help.