Sentence:  But Schnabel was a great teacher in addition to being a great performer , and the fact that <WSD>four</WSD> of the ten versions I listened to are by Schnabel pupils ( Clifford Curzon , Frank Glazer , Adrian Aeschbacher , and Victor Babin ) also sheds light on the master 's pedagogical skills . 
Meaning of the word marked with <WSD> tags:  being one more than three