In Operators§

See primary documentation in context for infix ⊄

multi sub infix:<>($a,$b --> Bool:D)

Not a subset of operator.

Returns True if $a is not a strict subset of $b. Equivalent to !(<).

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

In Sets, bags, and mixes§

See primary documentation in context for infix ⊄

Returns True if $a is not a strict subset of $b, else False. More information, Wikipedia definition.