Dilworth's Lemma
The Width of a set 
is equal to the minimum number of Chains neededto Cover . Equivalently, if a set of 
elements is Partially Ordered,then contains a Chain of size 
or an Antichain of size 
. Letting 
be theCardinality of , 
the Width, and 
the Length, this last statement says 
. Dilworth's lemma is a generalization of the Erdös-SzekeresTheorem. Ramsey's Theorem generalizes Dilworth's lemma.
- Quartile Range
- Quartile Skewness Coefficient
- Quartile Variation Coefficient
- Quasiamicable Pair
- Quasiconformal Map
- Quasigroup
- Quasiperfect Number
- Quasiperiodic Function
- Quasiperiodic Motion
- Quasirandom Sequence
- Quasiregular Polyhedron
- Quasirhombicosidodecahedron
- Quasirhombicuboctahedron
- Quasisimple Group
- Quasithin Theorem
- Quasitruncated Cuboctahedron
- Quasitruncated Dodecadocahedron
- Quasitruncated Dodecahedron
- Quasitruncated Great Stellated Dodecahedron
- Quasitruncated Hexahedron
- Quasitruncated Small Stellated Dodecahedron
- Quasi-Unipotent Group
- Quasi-Unipotent Problem
- Quaternary
- Quaternary Tree