Assertion: lens | /r/HasProperty | concave
Facets:
Source sentences:
text: A lens with two concave surfaces is biconcave (or just concave).
text: A lens is a piece of transparent material, usually circular in shape, with two polished surfaces, either or both of which is curved and may be either convex (bulging) or concave (depressed).
text: A lens with two concave surfaces is biconcave (or just concave).