2Sum is an easy Leetcode problem.
No easy Leetcode problems have an AC rate lower than 20 percent.  All Leetcode problems recommended to novices are easy.                                                                                                        Leetcode problems either have an AC rate lower than 20 percent or are starred by more than 1 thousand users.  All hard Leetcode problems are starred by more than 1 thousand users.  No Leetcode problems published after 2022 are starred by more than 1 thousand users.  2Sum is not recommended to novices and hard.  4Sum is either starred by more than 1 thousand users and published after 2022, or neither starred by more than 1 thousand users nor published after 2022. 
∀x (Easy(x) → ¬LowerAC(x)) ∀x (Recommended(x) → Easy(x)) ∀x (LowerAC(x) ⊕ Starred(x)) ∀x (Hard(x) → Starred(x)) ∀x (PublishedAfter2022(x) → ¬Starred(x)) ¬(Recommended(twosum) ∧ Hard(twosum)) ¬(Starred(foursum) ⊕ PublishedAfter2022(foursum))