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

Lemma lg_eql_lg : forall l1 l2, Q_Cong l1 -> EqL l1 l2 -> Q_Cong l2.