I wonder the following reduction is correct.
I'm trying to show that the following problem "PRINT_BLANK" is not decidable.
Input: (a coding of) Turing machine M. Question: Does the machine never types "blank" on the stripe when it runs on x?
An attempt for reduction: $AcceptProblem \leq PrintBlank: f(\langle M,x\rangle)= M'.$
Given $M$ and $x$, we'll construct $M'$: For an input $y$ for $M'_x$, $M'_x$ simulates running of M on $w$. if $M$ accepts $w$, $M'_x$ writes "blank" and accepts y, otherwise it writes $x$ itself on the tape and rejects.