# Glossary

## Index

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# D

## Differentiae

### 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).

## Directed arc

### 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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