R is symmetric as (L1, L2) ∈ R
⇒
L1 is perpendicular to L2
⇒
L2 is perpendicular to L1
⇒
(L2, L1) ∈ R R is not transitive Indeed, if L1 is perpendicular to L2 and
L2 is perpendicular to L3, then L1 can never be perpendicular to
L3 In fact, L1 is parallel to L3, i