| http://www.w3.org/ns/prov#value | - For example, what can be used is a plate made of a transparent organic or inorganic material including powder of at least one other transparent organic or inorganic material in well dispersed state, a transparent plate including suitable amount of fine voids or, a transparent plate having a plurality of convex lenses, concave lenses, or projections of complex forms at one side or both sides thereo
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