intersections called '''projective conic''' acknowledgement work jakob steiner referred steiner conic suppose projectivity formed two perspectivities centered points ''a'' ''b'' relating ''x'' ''x'' intermediary ''p'' math x overset doublebarwedge p overset b doublebarwedge x math projectivity math x barwedge x math given projectivity math barwedge math induced conic math c barwedge bigcup xx cdot yy x barwedge x land barwedge math given
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