Aver

дока́зывать

dokázyvatʹ

(to prove or justify (an allegation or plea that one has made))

заявля́ть

zajavljátʹ

(to assert the truth of (something); to affirm (something) with confidence; to declare (something) in a positive manner)

утвержда́ть

utverždátʹ

(to assert the truth of (something); to affirm (something) with confidence; to declare (something) in a positive manner)