Hz66 404 patch 2 (#614)

* add Set_operators demonstration

* Create L_union.md

* Update Set_operators.ipynb add badge and title

* Create L_intersect.md

* fixed badge Set_operators.ipynb

* Create L_subset.md

* Update Set_operators.ipynb

Changed "subset" italics issue

* Update Set_operators.ipynb

fix the grammar

* Create L_subsetEq.md

* Update L_subsetEq.md

* Create L_supset.md

* Create L_supsetEq.md

* Update L_supset.md

* Update Set_operators.ipynb

update the last subset to subsetEq / some grammar changed

* Update Set_operators.ipynb

* add L_in.md

* Delete docs/notebooks/Set_operators.ipynb

this file lack of "in" this keyword

* new Set_operators demonstration

* Update Set_operators.ipynb add badge and title

* Update L_in.md changed links

* Update L_intersect.md changed links

* Update L_subset.md changed links

* Update L_subsetEq.md changed links

* Update L_supset.md changed links

* Update L_supsetEq.md changed links

* Update L_union.md changed links

* add Partition_operators.ipynb

* Update Partition_operators.ipynb with title and badge

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Co-authored-by: N-J-Martin <146941515+N-J-Martin@users.noreply.github.com>