Double Acute Accent (˝)

𝔽˝ 𝕩: Insert

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Fold over cells of 𝕩 with 𝔽 from end to start, that is, insert 𝔽 between the major cells of 𝕩.

↗️
    a ← 3‿3 ⥊ ↕9

    +˝ a
⟨ 9 12 15 ⟩

    0‿1‿2 + 3‿4‿5 + 6‿7‿8
⟨ 9 12 15 ⟩

𝕨 𝔽˝ 𝕩: Insert With Initial

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Monadic insert, but use 𝕨 as initial right argument.

If

↗️
    b ← 3‿3 ⥊ ↕9

    1‿1‿1 +˝ b
⟨ 10 13 16 ⟩

    1 +˝ b
⟨ 10 13 16 ⟩

    0‿1‿2 + 3‿4‿5 + 6‿7‿8 + 1‿1‿1
⟨ 10 13 16 ⟩