diff --git a/.vscode/settings.json b/.vscode/settings.json
deleted file mode 100644
index 41a1aa3..0000000
--- a/.vscode/settings.json
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-    "cSpell.words": [
-        "elif"
-    ]
-}
\ No newline at end of file
diff --git a/Computer_Architecture/Hardware_abstraction.md b/Computer_Architecture/Hardware_abstraction.md
new file mode 100644
index 0000000..e69de29
diff --git a/Logic/_Laws_and_theorems.md/Corresponding_material_and_biconditional.md b/Logic/Laws_and_theorems.md/Corresponding_material_and_biconditional.md
similarity index 100%
rename from Logic/_Laws_and_theorems.md/Corresponding_material_and_biconditional.md
rename to Logic/Laws_and_theorems.md/Corresponding_material_and_biconditional.md
diff --git a/Logic/_Laws_and_theorems.md/DeMorgan's_Laws.md b/Logic/Laws_and_theorems.md/DeMorgan's_Laws.md
similarity index 100%
rename from Logic/_Laws_and_theorems.md/DeMorgan's_Laws.md
rename to Logic/Laws_and_theorems.md/DeMorgan's_Laws.md
diff --git a/Logic/_Laws_and_theorems.md/Law_of_Non-Contradiction.md b/Logic/Laws_and_theorems.md/Law_of_Non-Contradiction.md
similarity index 100%
rename from Logic/_Laws_and_theorems.md/Law_of_Non-Contradiction.md
rename to Logic/Laws_and_theorems.md/Law_of_Non-Contradiction.md
diff --git a/Logic/_Laws_and_theorems.md/Law_of_the_Excluded_Middle.md b/Logic/Laws_and_theorems.md/Law_of_the_Excluded_Middle.md
similarity index 100%
rename from Logic/_Laws_and_theorems.md/Law_of_the_Excluded_Middle.md
rename to Logic/Laws_and_theorems.md/Law_of_the_Excluded_Middle.md
diff --git a/Logic/_Laws_and_theorems.md/Theorems_and_empty_sets.md b/Logic/Laws_and_theorems.md/Theorems_and_empty_sets.md
similarity index 100%
rename from Logic/_Laws_and_theorems.md/Theorems_and_empty_sets.md
rename to Logic/Laws_and_theorems.md/Theorems_and_empty_sets.md
diff --git a/_meta/Resources.md b/_meta/Resources.md
index 6e25af1..a03d9d3 100644
--- a/_meta/Resources.md
+++ b/_meta/Resources.md
@@ -50,6 +50,8 @@ Hennesy, Patterson. 2020. **Computer Organization and Design** ([BBC O'Reilly Li
 
 Bryant, O'Halloran. 2016. **Computer Systems: A Programmer's Perspective**
 
+N.Nisan, S.Schoken. 2021. **The Elements of Computing Systems** (Second Edition)
+
 [How do transistors work, anyway?](https://lcamtuf.substack.com/p/how-do-transistors-work-anyway)
 
 [NAND latch](http://hyperphysics.phy-astr.gsu.edu/hbase/Electronic/nandlatch.html)
@@ -93,3 +95,5 @@ A. Sweighart. 2015. **Automate the Boring Stuff with Python**
 ## Shell
 
 B. Perry, D. Taylor. 2015. **Wicked Cool Shell Scripts**
+
+[What is the difference between `${var}`, `"$var"`, and `"${var}"` in the Bash shell? (Stack Overflow)](https://stackoverflow.com/q/18135451/10484600)