In Operators§

See primary documentation in context for infix (cont), infix ∋

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

Membership operator.

Returns True if $a contains $b as an element.

say (1,2,3(cont) 2# OUTPUT: «True␤» 
say (123 4;    # OUTPUT: «False␤» 

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

In Sets, bags, and mixes§

See primary documentation in context for infix (cont), infix ∋

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