. . "ruled" . . "ruled geometry" . . "ruled geometrical forms" . "generators of the ruling" . . . . "Ruled surface" . . . . "lines on a hyperboloid" . "conical bilinear complexes" . "ruled-surface" . . "ruled surfaces" . "regulated geometry" . "doubly-ruled surface" . "doubly ruled surface" . "ruled surface" . "Conical bilinear complexes" . . "Ruled surface" .