Question: Were Pietro Mascagni and Ambroise Thomas both best known for their contrabution to theatre? 
Sentence (from "Ambroise Thomas"): Charles Louis Ambroise Thomas (5 August 1811 – 12 February 1896) was a French composer, best known for his operas "Mignon" (1866) and "Hamlet" (1868, after Shakespeare) and as Director of the Conservatoire de Paris from 1871 till his death.
Relevant evidence: Yes