Huygens (1629-1695), [162]
Hyperbola, [110], [111], [113], [114], [115], 116, [117], [118], [162]
Imaginary elements, [146], [180], [181], 182, [185]
Infinitely distant elements, [6], [9], 22, [39], [40], [41], [104], [107], [110]
Infinity, [4], [5], [10], [12], [13], [14], [15], 17, [18], [19], [20], [21], [22], [41]
Involution, [37], [123], [124], [125], [126], 127, [128], [129], [130], [131], [132], [133], 134, [135], [136], [137], [138], [139], [140], 161, [163], [170]
Kepler (1571-1630), [162]
Lagrange (1736-1813), [176], [179]
Laplace (1749-1827), [179]