Assertion: blackboard eraser | /r/HasProperty | effective
Facets:
value: in actual class use
type: OTHER
value: in cleaning blackboards
type: PURPOSE
Source sentences:
text: It is, therefore, an outstanding object of the invention to provide a blackboard eraser which is effective in cleaning blackboards.
text: It is a further object of the invention to provide a blackboard eraser which is as effective in actual class use as in custodial use.