Two sets have the "same" (or "equal") cardinality if and only if they have the same number of elements, which is the another way of saying that there is a 1-to-1 correspondence between the two sets. The cardinality of the set "A" is "less than or equal to" the cardinality of set "B" if and only if there is an injective function from "A" to "B". The cardinality of the set "B" is "greater than or equal to" the cardinality of set "A" if and only if there is an injective function from "A" to "B". 