摘要：A real affine plane A2 is called an isotropic plane I2, if in A2 a metric is induced by an absolute {f, F}, consisting of the line at infinity f of A2 and a point F ∈ f. In this paper the well-known Butterfly theorem has been adapted for the isotropic plane. For the theorem that we will further-on call an Isotropic butterfly theorem, four proofs are given.
