Say, declare, define is the simple proof.
"declare/define" is only ONE note of infallibility. But this comes from the Holy Office and not from the Pope teaching
ex cathedra to the Universal Church. And the pope doesn't communicate infallibility to those whom he authorizes or approves (e.g. Bishops, Cardinals, Curia, Holy Office). Had this same language appeared in a Bull written by a Pope, then it would certainly be infallible.