Assertion: piano's hammer | /r/HasProperty | covered with felt
Facets:
Source sentences:
text: Modern hammers are covered with felt; earlier, leather was used.
text: The hammers are covered with felt which is a mixture of wool, silk and hair.
text: The hammers are covered with felt which is a mixture of wool, silk and hair.
text: Each piano key is connected to a hammer covered with felt.