Assertion: lens's shape | /r/HasProperty | paraboloid
Facets:
value: in order to convert a spherically expanding wavefront
type: PURPOSE
Source sentences:
text: In order to convert a spherically expanding wavefront into a spherically converging one using only a single boundary between the constituent explosives, the boundary shape must be a paraboloid; similarly, to convert a spherically diverging front into a flat one, the boundary shape must be a hyperboloid, and so on.