Projective theorems, [40], [104]

Quadrangle, [26], [27], [28], [29]

Quadric cone, [59]

Quadrilateral, [88], [95], [96]

Roberval (1602-1675), [168]

Ruler construction, [40]

Scheiner, [169]

Self-corresponding elements, [47], 48, [49], [50], [51]

Self-dual, [105]

Self-polar triangle, [102]