Sentence:  In a long commentary which he has inserted in the published text of the first <WSD>act</WSD> of the play , he says at one point : `` However , that experience never raised a doubt in his mind as to the reality of the underworld or the existence of Lucifer 's many faced lieutenants . 
Meaning of the word marked with <WSD> tags:  a subdivision of a play or opera or ballet