fix(guide): simplify directory structure

guide/english/logic/satisfiability/index.md

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+---
+title: Satisfiability
+---
+## Satisfiability
+
+<!-- The article goes here, in GitHub-flavored Markdown. Feel free to add YouTube videos, images, and CodePen/JSBin embeds  -->
+
+A formula P is considered **satisfiable** if it is **sometimes** true for some assignment of true/false to the variables.
+
+Example:
+  - x ^ y : is Satisfiable with x = T, y = T
+  - x v y -> x : is Satisfiable with x = T, y = F
+  
+If there are no assignments, then it is considered Unsatisfiable.
+
+
+
+#### More Information:
+<!-- Please add any articles you think might be helpful to read before writing the article -->