∀ {x : Lean.IR.VarId} {i : ℕ} {y : Lean.IR.Arg} {b : Lean.IR.FnBody} {x_1 : Lean.IR.VarId} {i_1 : ℕ} {y_1 : Lean.IR.Arg}
  {b_1 : Lean.IR.FnBody},
  Lean.IR.FnBody.set x i y b = Lean.IR.FnBody.set x_1 i_1 y_1 b_1 → x = x_1 ∧ i = i_1 ∧ y = y_1 ∧ b = b_1