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euler(Flat) -- Euler characteristic

Synopsis

Description

The beta invariant of an arrangement A is, by definition, the Euler characteristic of complement of A in complex projective space.

The beta invariant of a flat F is the beta invariant of the restriction of A to F.

i1 : A = typeA(3)

o1 = A

o1 : Hyperplane Arrangement 
i2 : euler A -- for a real arrangement, equals number of bounded chambers

o2 = 2