Suppose that $x^*$ satisfies $x^*\succsim x$ for $\forall x\in\{{x∈X|p·x\leq m}\}$.
How can we prove that $x\succsim x^*$ $\Rightarrow$ $p·x≥m$ if $\succsim$ is locally nonsatiated?
My idea for this goes like this but I am not sure:
Suppose that there exists $x' ∈ X$ such that $x'\succsim x^∗$ and $p · x' < m.$ Since we have local nonsatiation, for any $\epsilon>0$ there exists $x''\in X$ such that $||x''−x'||≤\epsilon$ and $x''\succ x'$. By transitivity of $\succsim$ and by $x''\succ x'\succsim x^*$. The former implies, by $p·x' < m$, that we can choose $\epsilon$ small enough such that $p·x'' < m$ and hence $x''\in\{{x∈X|p·x\leq m}\}$. This implies, by the definition of $x^∗$, that $x^∗\succsim x''$, a contradiction.