Proof that a given function is not a OWF
The attacker is given $y = f(v,w)$ and must find $v$ and $w$. The attacker can generate a random $v_0$ and calculate $g(v_0)$; then they can simply calculate $w_0=y⊕g(v_0)$ and then return $(v_0,w_0)$, for which $f(v_0,w_0)=y  \implies \Pr[\mathit{Invert}=1]=1&gt;\mathit{negl}(n)$.