+ destruct X.
+ destruct s as [vars vars_pf].
+
+ refine (bind localvars = fresh_lemma' _ (unleaves (vec2list (sac_types sac _ avars))) vars
+ (mapOptionTree weakLT' (pcb_freevars pcb)) (weakLT' ○ ξ) (weakL' lev) _ ; _).
+ apply FreshMon.
+ rewrite vars_pf.
+ rewrite <- mapOptionTree_compose.
+ reflexivity.
+ destruct localvars as [localvars [localvars_pf1 [localvars_pf2 localvars_dist ]]].
+ set (mapOptionTree (@fst _ _) localvars) as localvars'.
+
+ set (list2vec (leaves localvars')) as localvars''.
+ cut (length (leaves localvars') = sac_numExprVars sac). intro H''.
+ rewrite H'' in localvars''.
+ cut (distinct (vec2list localvars'')). intro H'''.
+ set (@Build_StrongCaseBranchWithVVs _ _ _ _ avars sac localvars'' H''') as scb.
+
+ refine (bind q = (f (scbwv_ξ scb ξ lev) (vars,,(unleaves (vec2list (scbwv_exprvars scb)))) _) ; return _).
+ apply FreshMon.
+ simpl.
+ unfold scbwv_ξ.
+ rewrite vars_pf.
+ rewrite <- mapOptionTree_compose.
+ clear localvars_pf1.
+ simpl.
+ rewrite mapleaves'.
+
+ admit.
+
+ exists scb.
+ apply ileaf in q.
+ apply q.
+
+ admit.
+ admit.
+ Defined.
+
+ Definition gather_branch_variables
+ Γ Δ (ξ:VV -> LeveledHaskType Γ ★) tc avars tbranches lev (alts:Tree ?? {sac : StrongAltCon &
+ ProofCaseBranch tc Γ Δ lev tbranches avars sac})
+ :
+ forall vars,
+ mapOptionTreeAndFlatten (fun x => pcb_freevars(Γ:=Γ) (projT2 x)) alts = mapOptionTree ξ vars
+ -> ITree Judg judg2exprType (mapOptionTree (fun x => pcb_judg (projT2 x)) alts)
+ -> ITree _ (fun q => prod (judg2exprType (pcb_judg (projT2 q)))
+ { vars' : _ & pcb_freevars (projT2 q) = mapOptionTree ξ vars' })
+ alts.
+ induction alts;
+ intro vars;
+ intro pf;
+ intro source.
+ destruct a; [ idtac | apply INone ].
+ simpl in *.
+ apply ileaf in source.
+ apply ILeaf.
+ destruct s as [sac pcb].
+ simpl in *.
+ split.