Solution
= Solution
For a <European call option>, the pointwise inequality $(S_T-K)^+\geq S_T-K$ and <risk-neutral pricing> give
$$
V_0\geq e^{-rT}(\mathbb E_{\mathbb Q}S_T-K)
=e^{-rT}(S_0e^{rT}-K)
=\boxed{S_0-e^{-rT}K}.
$$
= Solution
For a <European call option>, the pointwise inequality $(S_T-K)^+\geq S_T-K$ and <risk-neutral pricing> give
$$
V_0\geq e^{-rT}(\mathbb E_{\mathbb Q}S_T-K)
=e^{-rT}(S_0e^{rT}-K)
=\boxed{S_0-e^{-rT}K}.
$$