Let x0 of type ι be given.
Apply Field_of_RealsStruct_1f with
x0,
λ x1 x2 : ι → ι → ι . ∀ x3 . x3 ∈ field0 x0 ⟶ ∀ x4 . x4 ∈ field0 x0 ⟶ ∀ x5 . x5 ∈ field0 x0 ⟶ x1 x3 x5 = x1 x4 x5 ⟶ x3 = x4 leaving 2 subgoals.
The subproof is completed by applying H0.