Section Length_4.
Context `{TnEQD:Tarski_neutral_dimensionless_with_decidable_point_equality}.
Notation "l1 =l= l2" := (EqL l1 l2) (at level 80, right associativity).

Lemma null_len : forall A B la lb, Len A A la -> Len B B lb -> EqL la lb.