# isSink -- determines if a vertex of a digraph is a sink or not

## Synopsis

• Usage:
r = isSink (D, v)
• Inputs:
• D, an instance of the type Digraph,
• v, , the vertex being texted
• Outputs:
• r, , whether the vertex v is a sink or not

## Description

A vertex v of a Digraph D is a sink if v has no children

 i1 : D = digraph({a,b,c,d,e},{{a,b},{b,c},{b,d},{e,b}}); i2 : isSink (D,b) o2 = false i3 : isSink (D,d) o3 = true