Prove that \(I {\ \land \ }B \to V > 0\).
\[\begin{split} & I {\ \land \ }B \to V \gt 0\\ \iff & (i \leq n+1) {\ \land \ }(res = (i-1)!) {\ \land \ }(i \leq n) \to n-i+1 \gt 0 \\ \iff & (i \leq n) {\ \land \ }(res = (i-1)!) \to n-i \geq 0 \\ \iff & (i \leq n) \to n-i \geq 0 \\ \iff & \top \end{split}\]
It is now easy to see that the variant is bounded from below.