wrap up unimportant first two lectures in details tags

uni/mmme/1029_materials_and_manufacturing/materials.md

@@ -7,8 +7,13 @@ tags: [ uni, nottingham, mechanical, engineering, mmme1029, materials ]
 
 \tableofcontents
 
+<details>
+<summary>
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 # Lecture 1 (2021-10-04)
 
+</summary>
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 ## 1A Reading Notes
 
 ### Classification of Energy-Related Materials
@@ -107,8 +112,15 @@ work:
 
    > Young's modulus, specific heat, coefficient of thermal expansion
 
+</details>
+
+<details>
+<summary>
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 # Lecture 2
 
+</summary>
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 ## Properties of the Classes
 
 ### Metals
@@ -264,6 +276,8 @@ $$\rho = \frac m v$$
 
 > ~~C~~ B
 
+</details>
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 # Polymers
 
 ## Introduction to Polymers