Hilbert Hotel
Let a hotel have a Denumerable set of rooms numbered 1, 2, 3, .... Then any finitenumber 
of guests can be accommodated without evicting the current guests by moving the current guests from room
to room 
. Furthermore, a Denumerable number of guests can be similarlyaccommodated by moving the existing guests from to 
, freeing up a Denumerablenumber of rooms 
.
References
Lauwerier, H. ``Hilbert Hotel.'' In Fractals: Endlessly Repeated Geometric Figures. Princeton, NJ: Princeton University Press, p. 22, 1991. Pappas, T. ``Hotel Infinity.'' The Joy of Mathematics. San Carlos, CA: Wide World Publ./Tetra, p. 37, 1989.
- Cycloid Evolute
- Cycloid Involute
- Cycloid Radial Curve
- Cyclomatic Number
- Cyclotomic Equation
- Cyclotomic Factorization
- Cyclotomic Field
- Cyclotomic Integer
- Cyclotomic Invariant
- Cyclotomic Number
- Cyclotomic Polynomial
- Cylinder
- Cylinder Cutting
- Cylinder-Cylinder Intersection
- Cylinder Function
- Cylinder-Sphere Intersection
- Cylindrical Coordinates
- Cylindrical Equal-Area Projection
- Cylindrical Equidistant Projection
- Cylindrical Function
- Cylindrical Harmonics
- Cylindrical Hoof
- Cylindrical Projection
- Cylindrical Segment
- Cylindrical Wedge