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Plücker coordinates
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=== Line families === Because the [[Klein quadric]] is in {{tmath|\mathbb P^5}}, it contains linear subspaces of dimensions one and two (but no higher). These correspond to one- and two-parameter families of lines in {{tmath|\mathbb P^3}}. For example, suppose {{mvar|L, L′}} are distinct lines in {{tmath|\mathbb P^3}} determined by points {{math|'''x''', '''y'''}} and {{math|'''x'''′, '''y'''′}}, respectively. Linear combinations of their determining points give linear combinations of their Plücker coordinates, generating a one-parameter family of lines containing {{mvar|L}} and {{math|''L''′}}. This corresponds to a one-dimensional linear subspace belonging to the Klein quadric. ==== Lines in plane ==== If three distinct and non-parallel lines are coplanar; their linear combinations generate a two-parameter family of lines, all the lines in the plane. This corresponds to a two-dimensional linear subspace belonging to the Klein quadric. ==== Lines through point ==== If three distinct and non-coplanar lines intersect in a point, their linear combinations generate a two-parameter family of lines, all the lines through the point. This also corresponds to a two-dimensional linear subspace belonging to the Klein quadric. ==== Ruled surface ==== A [[ruled surface]] is a family of lines that is not necessarily linear. It corresponds to a curve on the Klein quadric. For example, a [[hyperboloid of one sheet]] is a quadric surface in {{tmath|\mathbb P^3}} ruled by two different families of lines, one line of each passing through each point of the surface; each family corresponds under the Plücker map to a [[conic section]] within the Klein quadric in {{tmath|\mathbb P^5}}.
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