∀ {R : Type u_1} [inst : CommRing R] {P : Type u_2} [inst_1 : CommRing P] [inst_2 : Algebra R P] {x : P}
  (motive : (∃ x', (algebraMap R P) x' = x) → Prop) (x_1 : ∃ x', (algebraMap R P) x' = x),
  (∀ (x' : R) (h : (algebraMap R P) x' = x), motive ⋯) → motive x_1