*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

           a ← 3‿3 ⥊ ↕9

           ∊ a

    
    
## `𝕨 ∊ 𝕩`: Member Of
    
Is each element in `𝕨` a major cell of `𝕩`?
    
           ⟨1⟩ ∊ ↕9

           a ← 3‿3 ⥊ ↕9

           ⟨0‿1‿2⟩ ∊ a

           ⟨1‿3 ⥊ 0‿1‿2⟩ ∊ a