Complex sentence: With Russell's discovery (1901,1902) According to van Heijenoort 1967:124, Russell discovered the paradox in June 1901 but did not report it until he wrote his letter to Frege dated 16 June 1902.
Split into simpler sentences: With Russell's discovery (1901,1902) According to van Heijenoort 1967:124, Russell discovered the paradox in June 1901. But Russell did not report it to Frege until his letter to Frege dated 16 June 1902.