English
By induction, the block memPartitionSet(f,n,a) belongs to memPartition(f,n).
Русский
По индукции блок memPartitionSet(f,n,a) принадлежит memPartition(f,n).
LaTeX
$$$\\operatorname{memPartitionSet}(f,n,a) \\in \\operatorname{memPartition}(f,n).$$$
Lean4
theorem memPartitionSet_mem (f : ℕ → Set α) (n : ℕ) (a : α) : memPartitionSet f n a ∈ memPartition f n := by
induction n with
| zero => simp [memPartitionSet]
| succ n ih =>
classical
rw [memPartitionSet_succ, memPartition_succ]
refine ⟨memPartitionSet f n a, ?_⟩
split_ifs <;> simp [ih]