fact: Definition incircle2d_exact x1 y1 x2 y2 x3 y3 x4 y4 := (let X1 := x1 - x4 in let X2 := x2 - x4 in let X3 := x3 - x4 in let Y1 := y1 - y4 in let Y2 := y2 - y4 in let Y3 := y3 - y4 in let Z1 := X1 * X1 + Y1 * Y1 in let Z2 := X2 * X2 + Y2 * Y2 in let Z3 := X3 * X3 + Y3 * Y3 in (X1 * Y2 - X2 * Y1) * Z3 + (X2 * Y3 - X3 * Y2) * Z1 + (X3 * Y1 - X1 * Y3) * Z2)%R.
imports: Reals Psatz Flocq(Core Operations Relative Plus_error)