Blaschke's Theorem
A convex planar domain in which the minimal length is 
always contains a Circle of Radius 1/3.
References
Le Lionnais, F. Les nombres remarquables. Paris: Hermann, p. 25, 1983.
- Deltoid Evolute
- Deltoid Involute
- Deltoid Pedal Curve
- Deltoid Radial Curve
- de Mere's Problem
- Demlo Number
- de Moivre-Laplace Theorem
- de Moivre Number
- de Moivre's Identity
- de Moivre's Quintic
- de Morgan's and Bertrand's Test
- de Morgan's Duality Law
- de Morgan's Laws
- Dendrite Fractal
- Denjoy Integral
- Denominator
- Dense
- Density
- Density (Polygon)
- Density (Sequence)
- Denumerable Set
- Denumerably Infinite
- de Polignac's Conjecture
- Depth (Graph)
- Depth (Size)