Let $L$ be the set of all the straight lines in the plane. Let $G$ and $H$ be the following relations in $L$: $G =\{(l_1 ,l_2) :l_1\ \text{is parallel to}\ l_2\}$,
My attempt:
The symmetric property is true since if $ l_1 $ is parallel to $ l_2 $, then $ l_2 $ is parallel to $ l_1 $. And the same transitive, it is easily followed.
But the reflexive is not fulfilled, since a line is not parallel to itself.