#H (elim H) /2/ normalize #c #d #H1 #H2 #H3 @(trans_star … H3) /2/
qed.
+lemma star_decomp_l :
+ ∀A,R,x,y.star A R x y → x = y ∨ ∃z.R x z ∧ star A R z y.
+#A #R #x #y #Hstar elim Hstar
+[ #b #c #Hleft #Hright *
+ [ #H1 %2 @(ex_intro ?? c) % //
+ | * #x0 * #H1 #H2 %2 @(ex_intro ?? x0) % /2/ ]
+| /2/ ]
+qed.
+
+(* right associative version of star *)
+inductive starl (A:Type[0]) (R:relation A) : A → A → Prop ≝
+ |injl: ∀a,b,c.R a b → starl A R b c → starl A R a c
+ |refll: ∀a.starl A R a a.
+
+lemma starl_comp : ∀A,R,a,b,c.
+ starl A R a b → R b c → starl A R a c.
+#A #R #a #b #c #Hstar elim Hstar
+ [#a1 #b1 #c1 #Rab #sbc #Hind #a1 @(injl … Rab) @Hind //
+ |#a1 #Rac @(injl … Rac) //
+ ]
+qed.
+
+lemma star_compl : ∀A,R,a,b,c.
+ R a b → star A R b c → star A R a c.
+#A #R #a #b #c #Rab #Hstar elim Hstar
+ [#b1 #c1 #sbb1 #Rb1c1 #Hind @(inj … Rb1c1) @Hind
+ |@(inj … Rab) //
+ ]
+qed.
+
+lemma star_to_starl: ∀A,R,a,b.star A R a b → starl A R a b.
+#A #R #a #b #Hs elim Hs //
+#d #c #sad #Rdc #sad @(starl_comp … Rdc) //
+qed.
+
+lemma starl_to_star: ∀A,R,a,b.starl A R a b → star A R a b.
+#A #R #a #b #Hs elim Hs // -Hs -b -a
+#a #b #c #Rab #sbc #sbc @(star_compl … Rab) //
+qed.
+
+lemma star_ind_l :
+ ∀A:Type[0].∀R:relation A.∀Q:A → A → Prop.
+ (∀a.Q a a) →
+ (∀a,b,c.R a b → star A R b c → Q b c → Q a c) →
+ ∀a,b.star A R a b → Q a b.
+#A #R #Q #H1 #H2 #a #b #H0
+elim (star_to_starl ???? H0) // -H0 -b -a
+#a #b #c #Rab #slbc @H2 // @starl_to_star //
+qed.
+
(* RC and star *)
lemma TC_to_star: ∀A,R,a,b.TC A R a b → star A R a b.
#A #R #a1 #a2 #Ha12 elim Ha12 -a1 -a2 /2 width=3/
qed.
-fact TC_star_ind_dx_aux: ∀A,R. reflexive A R →
- ∀a2. ∀P:predicate A. P a2 →
- (∀a1,a. R a1 a → TC … R a a2 → P a → P a1) →
- ∀a1,a. TC … R a1 a → a = a2 → P a1.
-#A #R #HR #a2 #P #Ha2 #H #a1 #a #Ha1
+fact TC_ind_dx_aux: ∀A,R,a2. ∀P:predicate A.
+ (∀a1. R a1 a2 → P a1) →
+ (∀a1,a. R a1 a → TC … R a a2 → P a → P a1) →
+ ∀a1,a. TC … R a1 a → a = a2 → P a1.
+#A #R #a2 #P #H1 #H2 #a1 #a #Ha1
elim (TC_to_TC_dx ???? Ha1) -a1 -a
-[ #a #c #Hac #H destruct /3 width=4/
+[ #a #c #Hac #H destruct /2 width=1/
| #a #b #c #Hab #Hbc #IH #H destruct /3 width=4/
]
qed-.
+lemma TC_ind_dx: ∀A,R,a2. ∀P:predicate A.
+ (∀a1. R a1 a2 → P a1) →
+ (∀a1,a. R a1 a → TC … R a a2 → P a → P a1) →
+ ∀a1. TC … R a1 a2 → P a1.
+#A #R #a2 #P #H1 #H2 #a1 #Ha12
+@(TC_ind_dx_aux … H1 H2 … Ha12) //
+qed-.
+
+lemma TC_symmetric: ∀A,R. symmetric A R → symmetric A (TC … R).
+#A #R #HR #x #y #H @(TC_ind_dx ??????? H) -x /3 width=1/ /3 width=3/
+qed.
+
lemma TC_star_ind_dx: ∀A,R. reflexive A R →
∀a2. ∀P:predicate A. P a2 →
(∀a1,a. R a1 a → TC … R a a2 → P a → P a1) →
∀a1. TC … R a1 a2 → P a1.
#A #R #HR #a2 #P #Ha2 #H #a1 #Ha12
-@(TC_star_ind_dx_aux … HR … Ha2 H … Ha12) //
+@(TC_ind_dx … P ? H … Ha12) /3 width=4/
qed-.
definition Conf3: ∀A,B. relation2 A B → relation A → Prop ≝ λA,B,S,R.