Complex sentence: On June 13,1957, he and his family attempted to gain admission to the all-white Long Meadow Park swimming pool; once they were denied, he immediately appealed unsuccessfully to city recreation officers.
Split into simpler sentences: On June 13,1957, he and his family attempted to gain admission to the all-white Long Meadow Park swimming pool. When they were denied, he immediately appealed unsuccessfully to city recreation officers.