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*View this file with results and syntax highlighting [here](https://mlochbaum.github.io/BQN/help/∊markfirst memberof.html).*

# Element Of (`∊`)

`∊ 𝕩`: Unique Mask

Mark the first occurrence of each major cell in `𝕩` with a 1, and all other occurrences with a 0.

       ∊ 4‿5‿6‿6‿4‿7‿5
    ⟨ 1 1 1 0 0 1 0 ⟩
       a ← 3‿3 ⥊ ↕9
    ┌─       
    ╵ 0 1 2  
      3 4 5  
      6 7 8  
            ┘
       ∊ a
    ⟨ 1 1 1 ⟩


`𝕨 ∊ 𝕩`: Member Of

Is each element in `𝕨` a major cell of `𝕩`?

       ⟨1⟩ ∊ ↕9
    ⟨ 1 ⟩
       a ← 3‿3 ⥊ ↕9
    ┌─       
    ╵ 0 1 2  
      3 4 5  
      6 7 8  
            ┘
       ⟨0‿1‿2⟩ ∊ a
    ┌·   
    · 0  
        ┘
       ⟨1‿3 ⥊ 0‿1‿2⟩ ∊ a
    ⟨ 1 ⟩