Deleted 01.curriculum/01.physics-chemistry-biology/03.niv3/02.geometrical-optics/02.geometrical-optics-foundings/02.refractive-index/06.refractive-index-level-down/page.en.md, 01.curriculum/01.physics-chemistry-biology/03.niv3/02.geometrical-optics/02.geometrical-optics-foundings/02.refractive-index/06.refractive-index-level-down/page.es.md, 01.curriculum/01.physics-chemistry-biology/03.niv3/02.geometrical-optics/02.geometrical-optics-foundings/02.refractive-index/06.refractive-index-level-down/page.fr.md files