From language/setbagmix

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

From language/operators

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multi sub infix:<⊅>($a,$b --> Bool:D)

Not a superset of operator.

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

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