In Operators§

See primary documentation in context for infix (elem), infix ∈

multi infix:<(elem)>($a,$b --> Bool:D)

Membership operator.

Returns True if $a is an element of $b.

say 2 (elem) (123); # OUTPUT: «True␤» 
say 4  (123);      # OUTPUT: «False␤» 

Since release 2020.05, ∊ is an alias for this operator.

In Sets, bags, and mixes§

See primary documentation in context for infix (elem), infix ∈

Returns True if $a is an element of $b, else False. More information, Wikipedia definition.