| http://www.w3.org/ns/prov#value | - European Patent No. 0294122 discloses a display system including a projection screen comprising an integral shape of a transparent photopolymer comprising an array of graded refractive index lenses, each of these lenses being formed by a respective region of the sheet extending between the surfaces of the sheet with the refractive index, in each said region, varying gradually with radial distance
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