Matthew Milano added subsubsection_i_First_direction_by__.tex  about 9 years ago

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\subsubsection*{i}  First direction: by contradiction. We assume that $(\I,r',m') \vDash \varphi$ for all points $(r',m')$ that are S-reachable from $(r,m)$ while $(\I,r,m) \vDash \neg C_S \varphi$.   As $(\I,r,m) \vDash \neg C_S \varphi$, by definition there exists some $k$ such that $(\I,r,m) \vDash \neg E^k_S \varphi$. Thus there also $\exists i \in S(r,m)$ s.t. $(\I,r,m) \vDash \neg B^S_i$, remember this $i$, we'll use it later. As $(\I,r,m) \vDash \neg B^S_i$, $\exists (r',m')$ s.t. $r_i(m) = r'_i(m')$ and $i \in S(r',m')$ where $(\I, r', m') \vDash \neg \varphi$. But $(r',m')$ is only one $i$-hop away from $(r,m)$, and is thus clearly $S$-reachable