Query: Who was Hart's writing partner?
Context: The advent of electric lighting led to elaborate theater productions, and in the 1880s, New York City theaters on Broadway and along 42nd Street began featuring a new stage form that became known as the Broadway musical. Strongly influenced by the city's immigrants, productions such as those of Harrigan and Hart, George M. Cohan, and others used song in narratives that often reflected themes of hope and ambition.