Need solution for Ex 3 pg 87 of Second Edition :Computability, Complexity, and Languages Fundamentals of Theoretical Computer Science Martin D. Davis,Ron Sigal,Elaine J. Weyuker

Let us call a partially computable function g(x) extendable if there is a computable function fc X) such that f(x) = g(x) for all x for which g(x) J . Show that there is no algorithm for determining of a given z whether or not az(x) is extendable. [Hint: Exercise 8 of Section 4 shows that @(x, X) + 1 is not extendable. Find an extendable function k(x) such that the function h(x, t) = @(x,x) + 1 i f @(t, t)J. k(x) otherwise is partially computable.]