Mathematical Double-struck S (𝕊)

𝕊: Current Function

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A variable assigned to the current function block. 𝕤 accesses the same value but has a subject role.

𝕊 can be used for recursion.

↗️
    F ← {𝕊 0: 1; 𝕩 × 𝕊 𝕩-1} # Factorial
    F 5
120

    {𝕤‿𝕤}4
⟨ (function block) (function block) ⟩