Fano's axiom

Fano's axiom

[¦fä·nōz ′ak·sē·əm]
(mathematics)
The postulate that the points of intersection of the three possible pairs of opposite sides of any quadrilateral in a given projective plane are noncollinear; thus a projective plane satisfying Fano's axiom is not a Fano plane, and a Fano plane does not satisfy Fano's axiom.