Assertion: newtonian telescope's mirror | /r/HasProperty | difficult to make
Facets:
value: in those days
type: TEMPORAL
value: unfortunately
type: MANNER
value: much more
type: DEGREE
Source sentences:
text: Unfortunately, in those days, mirrors were much more difficult to make.
text: Thinner mirrors can be more difficult to make, and can require more time and labor, thus making them more expensive.