# Glossary## IndexA B C D E F G H I J K L M N O P Q R S T U V W X Y Z # D
## Index
### Context
A term used when talking about *methods of definition* of types.
### Definition
A *differentia* (pl. *differentiae*) is a
*difference* between two things. In other words, the
differentiae between a subtype and its supertype(s) tell us how the subtype
*differs* from its supertype(s).
### Explanation
When defining a subtype *by differentiae*, one first makes
reference to one or more supertypes, and then one lists all of the
differences ("*differentiae*") between the subtype and the
supertype(s).
### Context
A term in graph theory.
### Definition
A *directed arc* is an arc which
has a *direction*. The converse is an *undirected arc*,
which does not have a direction.
### Explanation
A *directed arc* goes *from* one node *to*
another node. In other words, it has a direction. An *undirected
arc* merely connects two nodes, without specifying any
direction.
All of the arcs in conceptual graphs are directed.
### Context
A term in discrete mathematics, and CG theory.
### Definition
"Dyadic" is an adjective meaning "of 2 X", where "X" is determined
by the context.
A *dyadic relation* is a relation which relates two concepts.
A *dyadic lambda expression* is a lambda expression which
has two formal parameters.
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