#A¹
A¹ denotes the affine line, which is Spec k[x] when working over a field.
Model structures on simplicial presheaves
A¹-fundamental groups of isotropic groups
Is it possible to prove Serre's Problem (the Quillen-Suslin theorem) via Motivic Homotopy Theory?
Diploma thesis abstract
Walk-through to Morel-Voevodsky A¹-homotopy theory, page 48-50