Question: Were Pietro Mascagni and Ambroise Thomas both best known for their contrabution to theatre? 
Sentence (from "Pietro Mascagni"): While it was often held that Mascagni, like Leoncavallo, was a "one-opera man" who could never repeat his first success, "L'amico Fritz" and "Iris" have remained in the repertoire in Europe (especially Italy) since their premieres.
Relevant evidence: No