I'll give it a try.
1.“the Roman Pontiff”
2. “speaks ex cathedra” (“that is, when in the discharge of his office as shepherd and teacher of all Christians, and by virtue of his supreme apostolic authority….”)
3. “he defines”
4. “that a doctrine concerning faith or morals”
5. “must be held by the whole Church”
1. It's the Apostolic constitution of Pope Pius XII
regarding a teaching of the Church, it's the pope speaking, first criteria is met.
2. "by the authority of our Lord Jesus Christ, of the Blessed Apostles Peter and Paul, and by our own authority"
, second criteria is met
3. "we pronounce, declare, and define it to be a divinely revealed dogma"
, third criteria is met
4. "that the Immaculate Mother of God, the ever Virgin Mary, having completed the course of her earthly life, was assumed body and soul into heavenly glory."
, fourth criteria is met
5. "and for the joy and exultation of the entire Church" "may be brought to the attention of the universal Church"
, fifth criteria is met.
All five criteria for papal infallibility are met, this is an infallible teaching of the Catholic Church.