Kreisel Conjecture
A Conjecture in Decidability theory which postulates that, if there is a uniform bound to thelengths of shortest proofs of instances of 
, then the universal generalization is necessarily provable in PeanoArithmetic. The Conjecture was proven true by M. Baaz in 1988 (Baaz and Pudlák 1993).
References
Baaz, M. and Pudlák P. ``Kreisel's Conjecture for Dawson, J. ``The Gödel Incompleteness Theorem from a Length of Proof Perspective.'' Amer. Math. Monthly 86, 740-747, 1979. Kreisel, G. ``On the Interpretation of Nonfinitistic Proofs, II.'' J. Symbolic Logic 17, 43-58, 1952.
. In Arithmetic, Proof Theory, and Computational Complexity, Papers from the Conference Held in Prague, July 2-5, 1991 (Ed. P. Clote and J. Krajicek). New York: Oxford University Press, pp. 30-60, 1993.
- Sink (Directed Graph)
- Sink (Map)
- Sinusoidal Projection
- Sinusoidal Spiral
- Sinusoidal Spiral Inverse Curve
- Sinusoidal Spiral Pedal Curve
- Sister Celine's Method
- Site Percolation
- Siteswap
- Six-Color Theorem
- Skein Relationship
- Skeleton
- Skeleton Division
- Skew Conic
- Skewes Number
- Skew Field
- Skew Lines
- Skewness
- Skew Polyomino
- Skew Quadrilateral
- Skew Symmetric Matrix
- Sklar's Theorem
- Skolem-Mahler-Lerch Theorem
- Skolem Paradox
- Skolem Sequence