Jason: [-2k=2k already imply k=0; therefore, further manipulation of 1/k is no longer valid (divided by zero).]

Wilson: [When the point get to -2k=2k, the equation is valid only if k=0.  k can no longer equal to any integer.  For n=k and n=k+1, the conclusion is that （n-2)²=n² is true if and only if n=0 or n=1]