Square Original Of (⊐)

⊐ 𝕩: Classify

First index of each major cell of 𝕩 in 𝕩.

       ⊐ 5‿6‿2‿2‿5‿1
⟨ 0 1 2 2 0 3 ⟩

       a ← 3‿3 ⥊ 0‿1‿2‿9‿0‿9‿0‿1‿2

       ⊐ a
⟨ 0 1 0 ⟩

𝕨 ⊐ 𝕩: Index Of

First index of each major cell of 𝕩 in 𝕨. Rank of 𝕩 must be at least cell rank of 𝕨`.

If a cell is not found in 𝕨, that position will contain the length of 𝕨 (≠𝕨).

       5‿6‿2‿2‿5‿1 ⊐ 5‿2‿1‿6
⟨ 0 2 5 1 ⟩

       a ← 3‿3 ⥊ 0‿1‿2‿9‿0‿9‿0‿1‿2
Error: Redefinition

       a ⊐ ⟨9‿0‿9⟩
┌·   
· 3  
    ┘