apply funext
t : TraceRel'
es : vset F SysEl
ρ : Config F
⊢ (fun x => ((fun x => (x.1.2, x.2)) '' fun e => e ∈ t ∧ (e.1.1, e.2) ∈ es) (x, ρ)) =
    (fun x => x.2) '' fun e => (e ∈ fun x => t (x, ρ)) ∧ e.1 ∈ fun x => es (x, ρ)
case h
t : TraceRel'
es : vset F SysEl
ρ : Config F
⊢ ∀ (x : GSNEl),
    ((fun x => (x.1.2, x.2)) '' fun e => e ∈ t ∧ (e.1.1, e.2) ∈ es) (x, ρ) =
      ((fun x => x.2) '' fun e => (e ∈ fun x => t (x, ρ)) ∧ e.1 ∈ fun x => es (x, ρ)) x