toRepresentation(a) is: new Set(1,2)
toRepresentation(b) is: new Set(1,2,new Set(1,2),99,3)
intersection(a, b) new Set(1,2)
subtract({value:a, from:b}) new Set(new Set(1,2),99,3)
subtract({value:[...a,a], from:b}) new Set(99,3)