WORKMENS COMPENSATION ? NOTICE IN WRITING ? APPEAL AND ERROR ? COURTS. 1. Workmens Compensation ? Notice ? Written. Provisions of statute requiring that injured employee give notice in writing to employer of injury unless employer has actual knowledge of such accident and injury are mandatory and compliance with its requirements are indispensable to maintenance of a claim for compensation. 2. Workmens Compensation ? Appeal and Error ? Affirmance of boards findings, when. In actions under the Workmens Compensation Act, Supreme Court - Page 14 must affirm findings of Industrial Accident Board and of district court, if evidence is sufficient to sustain findings of board and court, even though some conflict in the evidence may exist. 3. Workmens Compensation ? Province of trial court. Credibility of witnesses and weight of their testimony is exclusively for the trial court in compensation case. 4. Workmens Compensation ? Lack of notice ? Claim barred. In proceeding for compensation benefits by miner, who alleged that he sustained a back injury while lifting a piece of timber over his head, but who did not give written notice of injury or obtain a hospital ticket alleging injury until more than 30 days later and who filed a claim for insurance under his employers group insurance contract for nonoccupational ailments and drew benefits thereunder for about six weeks, evidence sustained finding that employer did not have actual knowledge of injury until more than 30 days thereafter and that claim was barred.