How is infinity defined?
There are different sizes of infinity. Two sets are said to have equal cardinality (=equal size) if there exists a one-on-one correspondence between them. A set A is said to have less or equal cardinality than B if there exists an injection [itex]A\rightarrow B[/itex]. So a set A has strictly less cardinality if there exists an injection [itex]A\rightarrow B[/itex] but there does not exists a bijection [itex]A\rightarrow B[/itex].ok and why can we say that there are more reals than naturals . I mean they are both infinite. I have seen cantors diagonal argument.