Original: He discovered or co-discovered several comets , including 23P/Brorsen-Metcalf and 97P/Metcalf-Brewington ; he also discovered a number of asteroids .
Simplified: He found or co-found many comets , such as 23P/Brorsen-Metcalf and 97P/Metcalf-Brewington ; he also found many asteroids .