T).(match us with [TNil \Rightarrow t | (TCons u ul) \Rightarrow (THead k u
(THeads k ul t))])) in THeads.
+definition tweight:
+ T \to nat
+\def
+ let rec tweight (t: T) on t: nat \def (match t with [(TSort _) \Rightarrow
+(S O) | (TLRef _) \Rightarrow (S O) | (THead _ u t0) \Rightarrow (S (plus
+(tweight u) (tweight t0)))]) in tweight.
+