English
For any Pell solution a = (x,y) in Pell.Solution₁ d, the Pell equation x^2 - d y^2 = 1 holds.
Русский
Для любого решения Пелля a = (x,y) в Pell.Solution₁ d выполняется тождество x^2 - d y^2 = 1.
LaTeX
$$$$ a.x^2 - d\, a.y^2 = 1. $$$$
Lean4
/-- The proof that `a` is a solution to the Pell equation `x^2 - d*y^2 = 1` -/
theorem prop (a : Solution₁ d) : a.x ^ 2 - d * a.y ^ 2 = 1 :=
is_pell_solution_iff_mem_unitary.mpr a.property