Complex sentence: He introduced the quark constituents of all hadrons, having first identified the SU (3) flavor symmetry of hadrons, now understood to underlie the light quarks, extending isospin to include strangeness, a quantum number which he also discovered.
Split into simpler sentences: He introduced the quark-constituents of all hadrons-having first identified the SU (3) flavor symmetry of hadrons. This symmetry is now understood to underlie the light quarks, extending isospin to include strangeness, a quantum number which he also discovered.