Y may be any array.  X may be any array.  R is Boolean. An element of R is 1 if the corresponding element of X can be found in Y.

An element of X is considered identical to an element in Y if X≡Y returns 1 for those elements.

⎕CT and ⎕DCT are implicit arguments of Membership.

Examples

      'THIS NOUN' ∊ 'THAT WORD'
1 1 0 0 1 0 1 0 0
 
      'CAT' 'DOG' 'MOUSE' ∊ 'CAT' 'FOX' 'DOG' 'LLAMA'
1 1 0

For performance information, see Search Functions and Hash Tables.