Recall that $H = (V', A')$ is a subdigraph of $D = (V,A)$ iff
a. $V' \subseteq V$
b. $A' \subseteq A$
c. If $vw \in A'$ then $\{v, w\} \subseteq V'$Describe what can go wrong if condition c is not included in the definition.
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I would be happy if anybody please help me in this case I am stuck here. Thanks in advance.
Well why not pick a simple graph and see what would happen with your own eyes?
Take the following graph for example:
You have $V=\{0,1,2\}$ and $A=\{01,12,20\}$.
Take $V'$ and $A'$ such that a. and b. are satisfied, but not c. For example: $V'=\{0,1\}$ and $A'=\{12\}$.
Try to draw the digraph $H'=(V',A')$ and you'll see what goes wrong.