Howell Design
Let 
be a set of 
symbols, then a Howell design 
on symbol set is an 
array 
such that
- 1. Every cell of is either empty or contains an unordered pair of symbols from ,
- 2. Every symbol of occurs once in each row and column of , and
- 3. Every unordered pair of symbols occurs in at most one cell of .
References
Colbourn, C. J. and Dinitz, J. H. (Eds.) ``Howell Designs.'' Ch. 26 in CRC Handbook of Combinatorial Designs. Boca Raton, FL: CRC Press, pp. 381-385, 1996.
- Spherical Frustum
- Spherical Geometry
- Spherical Hankel Function of the First Kind
- Spherical Hankel Function of the Second Kind
- Spherical Harmonic
- Spherical Harmonic Addition Theorem
- Spherical Harmonic Closure Relations
- Spherical Harmonic Tensor
- Spherical Helix
- Spherical Point System
- Spherical Polygon
- Spherical Ring
- Spherical Sector
- Spherical Segment
- Spherical Shell
- Spherical Spiral
- Spherical Symmetry
- Spherical Tessellation
- Spherical Triangle
- Spherical Trigonometry
- Spherical Vector Harmonic
- Spheroid
- Spheroidal Harmonic
- Spheroidal Wavefunction
- Sphinx