Check if each certificate in round 1 of a DAG has no predecessors.
This is an invariant of the DAGs of validators, as proved elsewhere.
Theorem:
(defthm dag-no-prodecessors-round-1-p-necc (implies (dag-no-prodecessors-round-1-p dag) (implies (and (in cert dag) (equal (certificate->round cert) 1)) (emptyp (predecessors cert dag)))))
Theorem:
(defthm booleanp-of-dag-no-prodecessors-round-1-p (b* ((yes/no (dag-no-prodecessors-round-1-p dag))) (booleanp yes/no)) :rule-classes :rewrite)