Translate major cells of 𝕩 to unique ID numbers based on first occurrence.

    ⊐ 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, the length of 𝕨 (≠𝕨) is used for that position.

    5‿6‿2‿2‿5‿1 ⊐ 5‿7‿1‿6
⟨ 0 6 5 1 ⟩

    b ← 3‿3 ⥊ 0‿1‿2‿9‿0‿9‿0‿1‿2

    b ⊐ ≍9‿0‿9
⟨ 1 ⟩

Square Original Of (`⊐`)