∀e:EuclideanPlane. EquivRel(ProperSegment;s,t.s ≡ t)
{ (Auto THEN RepeatFor 2 ((D 0 THEN Auto)) THEN EAuto 1) }
1. e : EuclideanPlane@i'
2. Sym(ProperSegment;s,t.s ≡ t)
3. a : ProperSegment@i
4. b : ProperSegment@i
5. c : ProperSegment@i
6. a ≡ b@i
7. b ≡ c@i
⊢ a ≡ c