Let $M=\{a, b, c \mid$, where $a, b, c$ are alphabetic characters. Let $F: M \rightarrow M$, with the values, $F(a)=b, F(b)=c, F(c)=a$. Write the recursive definition of a function, $r: N a t \rightarrow M$, which satisfies $r(0)=a$ and uses $M$ and $F$ as in the statement of the Recursion Theorem. Also, what are the values of $r(k)$ for
$$
k=s(0), \quad s(s(0)), \quad s(s(s(0))), \quad s(s(s(s(0)))), \quad s(s(s(s(s(0))))) ?
$$