Square Image Of (⊏)

⊏ 𝕩: First Cell

First major cell of 𝕩.

       ⊏ ⟨1, 2, 3⟩
┌·   
· 1  
    ┘

       a ← 3‿3 ⥊ ↕9

       ⊏ a
⟨ 0 1 2 ⟩

𝕨 ⊏ 𝕩: Select

Select the major cells of 𝕨 at the indices in 𝕩.

       2‿0 ⊏ ⟨1, 2, 3⟩
⟨ 3 1 ⟩

       b ← 3‿3 ⥊ ↕9

       2‿0 ⊏ b
┌─       
╵ 6 7 8  
  0 1 2  
        ┘