# parents -- returns the parents of a vertex on a digraph

## Synopsis

• Usage:
P = parents (D, v)
• Inputs:
• D, an instance of the type Digraph,
• v, , the vertex whose parents we want to find
• Outputs:
• P, a set, the parents of v

## Description

The parents of a vertex v in a digraph D are all the vertexSet u in D such that {u,v} is an edge of D. In other words, the parents of v are all the vertexSet that have edges coming out of them that point at v.

 i1 : D = digraph({a,b,c,d,e},{{a,b},{b,c},{b,d},{e,b}}); i2 : parents (D, b) o2 = set {a, e} o2 : Set