have hrw := Equiv.swap_image_eq_self
    (show e ∈ M.E ↔ f ∈ M.E by simp [h.mem_ground_left, h.mem_ground_right])
α : Type u_1
M N : Matroid α
e f g : α
I X P D : Set α
h : M.Parallel' e f
inst✝ : DecidableEq α
⊢ M.mapEquiv (Equiv.swap e f) = M
α : Type u_1
M N : Matroid α
e f g : α
I X P D : Set α
h : M.Parallel' e f
inst✝ : DecidableEq α
hrw : ⇑(Equiv.swap e f) '' M.E = M.E
⊢ M.mapEquiv (Equiv.swap e f) = M