bijection between closed and open interval
For mapping the end points of the closed unit interval and its inner points bijectively onto the corresponding open unit interval , one has to discern suitable denumerable subsets in both sets:
where
Then the mapping from to defined by
is apparently a bijection. This means the equicardinality of both intervals.
Note that the bijection is neither monotonic (e.g. , , ) nor continuous. Generally, there does not exist any continuous surjective
mapping , since by the intermediate value theorem a continuous function maps a closed interval to a closed interval.
References
- 1 S. Lipschutz: Set theory
. Schaum Publishing Co., New York (1964).