Proposition 5
Tag 097B, permanent. Cite it as [Bourbaki, Tag 097B].
Integration, chapter V, § 8. Products of measures
— Let be a numerical function , lower semi-continuous on . Then, the function
is lower semi-continuous on , and
This is a consequence of Prop. 2 of §3, No. 1, taking into account Lemma 1 of No. 1.
Bourbaki puts the proof directly after the statement, so what is above is the statement and its proof together.