Corollary 1
Tag 08TK, permanent. Cite it as [Bourbaki, Tag 08TK].
Integration, IV, p. 53, § 4. Integrable functions and sets
Let be a measure on ; the space is dense in each of the spaces ().
For, it follows from Prop. 19 and the criterion for convergence in mean for uniform limits of functions with compact support (§ 3, No. 3, Prop. 4) that is dense, for the topology of convergence in mean of order , in the closure of the space of continuous functions with compact support, whence the corollary.
Bourbaki puts the proof directly after the statement, so what is above is the statement and its proof together.