isSource -- determines if a vertex of a digraph is a source or not

• Usage:

  r = isSource (D, v)

• Inputs:
  • D, a digraph,
  • v, a thing, the vertex being texted
• Outputs:
  • r, a Boolean value, whether the vertex v is a source or not

i1 : D = digraph({a,b,c,d,e},{{a,b},{b,c},{b,d},{e,b}});

i2 : isSource (D,c)

o2 = false

i3 : isSource (D,e)

o3 = true