TITLE: Find all possible topological-sortings of graph G
QUESTION [5 upvotes]: A topological ordering of G is an ordering of the nodes as $v_1,v_2,...,v_n$ so that all edges point "forward": for every edge $(v_i,v_j)$, we have $i<j$.
Moreover, the first node in a topological ordering must be one that has no edge coming into it. Analogously, the last node must be one that has no edge leaving it.

What are the topological-sortings of the following graphs?
$G_1$:

Topological Sortings: (solution is from book, so it is correct)

a b c d e
a c b d e
a c d b e

Okay, so if I draw the graph like a "tree" we have:

Why is a topological-sorting [a c b d e] possible if there is no path from $c$ to $b$?
$G_2$:

Following the same rhythm from solution to $G_1$, I believe the following are all possible topological sortings in $G_2$:

a b c d e f
a b d c e f
a b d e c f
a d b c e f
a d b e c f
a d e b c f

REPLY [2 votes]: A tip for visualizing topological orders of (directed acyclic) graphs: 
You can visualize them by taking the (ordered) list of vertices, and drawing the edges of the graph between the elements. So for the first question, take the list [a c b d e], and draw out the edges (I'll follow your lead and give an illustration myself):

Notice that all edges indeed point "forward". Therefore we have, by your own definition, a topological order. As for the second part, I assume that Brian M. Scott's response suffices.