English
The x-coordinate of a Pell solution is the real part of its representation in Z[√d].
Русский
x-координата решения Пелля равна вещественной части его представления в Z[√d].
LaTeX
$$$$ a=(x,y) \in Pell.Solution_1(d) \implies a.x = x = \Re(a : \mathbb{Z}[\sqrt{d}]). $$$$
Lean4
/-- The `x` component of a solution to the Pell equation `x^2 - d*y^2 = 1` -/
protected def x (a : Solution₁ d) : ℤ :=
(a : ℤ√d).re