Two sets A and B have the same cardinality if there exists a bijection from A to B, that is, a function from A to B that is both invective and subjective.
if the two set have same cardinality then it is called equivalent set,. a={1,2,3} m={1,2,3} same credinality if two sets have same cardinality and same elements then it is called equal set.eg d={1,2,3,4} e={1,2,3,4} d and e are equal set same element and same credinality