diff --git a/document.pdf b/document.pdf index ec699b2..d081b2b 100644 Binary files a/document.pdf and b/document.pdf differ diff --git a/document.tex b/document.tex index 1725a44..48add82 100644 --- a/document.tex +++ b/document.tex @@ -173,6 +173,62 @@ S(T, P) = (\emptyset, \emptyset) \textrm{ (fixpoint reached)} \end{align*} + + \begin{proposition}\label{} + Given a poset $\langle \mathcal{L}, \leq \rangle$, + an operator $o: \mathcal{L} \rightarrow \mathcal{L}$ is $\leq$-monotone iff it is $\geq$-monotone + \end{proposition} + \begin{proof} + ($\Rightarrow$) + Initially, we have $\forall x, y \in \mathcal{L}: x \leq y \implies o(x) \leq o(y)$. + Let $a, b \in \mathcal{L}$ such that $a \geq b$. We have $b \leq a$ and can apply our initial assumption to get $o(b) \leq o(a)$. + This gives us $o(a) \geq o(b)$. + We can generalize to obtain $\forall x, y \in \mathcal{L}: x \geq y \implies o(x) \geq o(y)$. + ($\Leftarrow$) Proof is more or less the same + \end{proof} + + % Let $\leq$ and $\leq_i$ be the orderings over the set $\mathcal{L}^2$ such that for each ${(T, P), (X, Y) \in \mathcal{L}^2}$ + % \begin{align*} + % (a, b) \leq (x, y) &\textit{ iff } a \leq x \textrm{ and } b \leq y\\ + % (a, b) \leq_i (x, y) &\textit{ iff } a \leq x \textrm{ and } \boxed{y} \leq b + % \end{align*} + % \begin{proposition} + % Given a poset $\langle \mathcal{L}^2, \leq \rangle$, an operator $o: \wp(\mathcal{L})^2 \rightarrow \wp(\mathcal{L})^2$ is $\leq$-monotone iff it is $\leq_i$-monotone + % \end{proposition} + % \begin{proof} + % ($\Rightarrow$) Initially, we have ${\forall (x, y), (a, b) \in \mathcal{L}^2: (x, y) \leq (a, b) \implies o(x, y) \leq o(a, b)}$. + % If we rearrange the variables we get + % \begin{align*} + % &\forall x, a \in \mathcal{L}: \forall y, b \in \mathcal{L}:\\ + % &~~~~~(x \leq a \land y \leq b) \implies ((o_1(x, y) \leq o_1(a, b)) \land (o_2(x, y) \leq o_2(a, b))) + % \end{align*} + + + % Let $(u, v), (i, k) \in \mathcal{L}^2$ such that $(u, v) \leq_i (i, k)$. We have $(u, k) \leq (i, v)$. We can apply the initial assumption to obtain + % $o(u, k) \leq o(i, v)$. This is equivalent to + % \begin{align*} + % (o_1(u, k) \leq o_1(i, v)) \land (o_2(u, k) \leq o_2(i, v)) + % \end{align*} + % which can be rewritten as + % \begin{align*} + % (o_1(u, k) \leq o_1(i, v)) \land \boxed{(o_2(i, v)) \leq o_2(u, k))} + % \end{align*} + % \end{proof} + + \begin{proposition} + An operator $A : L^2 \rightarrow L^2$ is symmetric and monotone + with respect to both $\leq_i$ and $\leq$ if and only if there is a monotone operator + $O : L \rightarrow L$ such that for every $x, y \in L, A(x, y) = (O (x), O (y ))$ + \end{proposition} + \begin{proof} + ($\Rightarrow$) + From Proposition 5 and 6 we have for any $x \in L$, $A_1(\cdot, x)$ and $A_1(x, \cdot)$ are monotone and $A_1(x, \cdot)$ is antimonotone. + By Proposition 2, $A_1(x, \cdot)$ is constant, denote this constant as the function $O(x)$. + By the symmetric condition, we have $A_1(x, \cdot) = A_2(\cdot, x)$, thus $A(x, y) = (O(x), O(y))$. It follows from the monotonicity of $A$ that $O$ is monotone. + + ($\Leftarrow$) + Clearly $A$ is symmetric, and $\leq$-monotone (Given that $O$ is $\leq$-monotone). Using proposition 3.1 (above) $O(x)$ is $\geq$-monotone, thus $A$ is $\leq_i$-monotone as well. + \end{proof} \section{The Polynomial Heirarchy} Intuitive definitions of ${\sf NP}$