Answer:

proven

Answer	Crossword Clue
PROVEN	Like an ironclad case
PROVEN	Demonstrated
PROVEN	No longer in doubt

PROVEN	Established via evidence
PROVEN	Shown as true
PROVEN	Established
PROVEN	Demonstrated.
PROVEN	Tested.
PROVEN	Made clear.
PROVEN	Verified
PROVEN	Tried

PROVEN	Documented
PROVEN	Mathematically validated
PROVEN	Like Fermat's last theorem, eventually
PROVEN	Substantiated
PROVEN	Innocent until -- guilty
PROVEN	Shown to be a fact
PROVEN	Established as fact
PROVEN	Tried and true

PROVEN	QED
PROVEN	Marked with a "QED"