Species

A species of structures is a rule which

1. Produces, for each finite set , a finite set ,

2. Produces, for each bijection , a function

The functions should further satisfy the following functorial properties:

1. For all bijections and ,

2. For the Identity Map ,

An element is called an -structure on (or a structure of species on ). The function is called the transport of -structures along .
References

Bergeron, F.; Labelle, G.; and Leroux, P. Combinatorial Species and Tree-Like Structures. Cambridge, England: Cambridge University Press, p. 5, 1998.

• Diophantine Set
• Diophantus Property
• Diophantus' Riddle
• Dipyramid
• Dirac Delta Function
• Dirac Matrices
• Dirac's Theorem
• Directed Angle
• Directed Graph
• Directional Derivative
• Direction Cosine
• Directly Similar
• Director Curve
• Direct Product (Group)
• Direct Product (Matrix)
• Direct Product (Set)
• Direct Product (Tensor)
• Directrix (Conic Section)
• Directrix (Graph)
• Directrix (Ruled Surface)
• Direct Search Factorization
• Direct Sum (Module)
• Dirichlet Beta Function
• Dirichlet Boundary Conditions
• Dirichlet Conditions