+(* Normal form and strong normalization on unboxed triples ******************)
+
+inductive SN3 (A) (B) (C) (R,S:relation6 A B C A B C): relation3 A B C ≝
+| SN3_intro: ∀a1,b1,c1. (∀a2,b2,c2. R a1 b1 c1 a2 b2 c2 → (S a1 b1 c1 a2 b2 c2 → ⊥) → SN3 … R S a2 b2 c2) → SN3 … R S a1 b1 c1
+.
+