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The Fano plane is an example of an (n 3)-configuration, that is, a set of n points and n lines with three points on each line and three lines through each point. The Fano plane, a (7 3)-configuration, is unique and is the smallest such configuration. [11]
The Fano plane is the projective plane with the fewest points and lines. The smallest 2-dimensional projective geometry (that with the fewest points) is the Fano plane, which has 3 points on every line, with 7 points and 7 lines in all, having the following collinearities:
The Fano plane is a Steiner triple system S(2,3,7). The blocks are the 7 lines, each containing 3 points. Every pair of points belongs to a unique line. In combinatorial mathematics, a Steiner system (named after Jakob Steiner) is a type of block design, specifically a t-design with λ = 1 and t = 2 or (recently) t ≥ 2.
The Fano plane, discussed below, is denoted by PG(2, 2). The third example above is the projective plane PG(2, 3). The Fano plane. Points are shown as dots; lines are shown as lines or circles. The Fano plane is the projective plane arising from the field of two elements. It is the smallest projective plane, with only seven points and seven lines.
L 2 (7) ≅ L 3 (2) which acts on the 1 + 2 + 4 = 7 points of the Fano plane (projective plane over F 2); this can also be seen as the action on order 2 biplane, which is the complementary Fano plane. L 2 (11) is subtler, and elaborated below; it acts on the order 3 biplane. [8]
The adjunction formula implies that K D = (K X + D)| D = (−(n+1)H + deg(D)H)| D, where H is the class of a hyperplane. The hypersurface D is therefore Fano if and only if deg(D) < n+1. More generally, a smooth complete intersection of hypersurfaces in n-dimensional projective space is Fano if and only if the sum of their degrees is at most n.
This Frobenius group acts simply transitively on the 21 flags in the Fano plane, i.e. lines with marked points. The formulas for σ and τ on E thus "lift" the formulas on F 8. Mumford also obtains an action simply transitive on the vertices of the building by passing to a subgroup of Γ 1 = <ρ, σ, τ, −I>.
The Fano plane. This particular projective plane is sometimes called the Fano plane. If any of the lines is removed from the plane, along with the points on that line, the resulting geometry is the affine plane of order 2. The Fano plane is called the projective plane of order 2 because it is unique (up to