Turing-completeness of Goto language with limited constants
No, that is not a proof.  &quot;It seems obvious to me&quot; is not a proof.
To obtain a formal proof, describe an algorithm that, given a Goto program $P$, outputs a Goto$_{17}$ program $P'$, and prove that $P'$ simulates $P$.  Basically, you need to construct a compiler that compiles from Goto to Goto$_{17}$, and then prove it correct.