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*Definition:*
A *directed graph* is a pair <`V`,
`E`> of a set `V` of *vertices*/ *nodes* and
a set of `E` of *edges*/ *arcs* where `E` is
binary relation on `V`:

Gis directed graph : <=>existsV,E:G= <V,E> /\EsubsetVxV.

*Interpretation:*
<`x`, `y`> in `E`

`x`is connected to`y`in`G`,`x`is*initial node*of edge,`y`is*terminal node*of edge.

Author: Wolfgang Schreiner

Last Modification: January 26, 2000