-- Module: Mathlib.RingTheory.Spectrum.Prime.LTSeries
Goal:
R : Type u_1
inst : CommRing R
inst_1 : IsNoetherianRing R
x : R
n : ℕ
hn :
  ∀ (p : LTSeries (PrimeSpectrum R))
    (hx :
      x ∈
        (RelSeries.last (r :=
            {x : PrimeSpectrum R × PrimeSpectrum R |
              match (motive := PrimeSpectrum R × PrimeSpectrum R → Prop) x with
              | (a, b) => a < b})
            p).asIdeal)
    (hp :
      p.length (r :=
          {x : PrimeSpectrum R × PrimeSpectrum R |
            match (motive := PrimeSpectrum R × PrimeSpectrum R → Prop) x with
            | (a, b) => a < b}) =
        n),
    ∃ (q : LTSeries (PrimeSpectrum R)),
      x ∈
          (q.toFun (r :=
              {x : PrimeSpectrum R × PrimeSpectrum R |
                match (motive := PrimeSpectrum R × PrimeSpectrum R → Prop) x with
                | (a, b) => a < b})
              1).asIdeal ∧
        n =
            q.length (r :=
              {x : PrimeSpectrum R × PrimeSpectrum R |
                match (motive := PrimeSpectrum R × PrimeSpectrum R → Prop) x with
                | (a, b) => a < b}) ∧
          RelSeries.head (r :=
                {x : PrimeSpectrum R × PrimeSpectrum R |
                  match (motive := PrimeSpectrum R × PrimeSpectrum R → Prop) x with
                  | (a, b) => a < b})
                p =
              RelSeries.head (r :=
                {x : PrimeSpectrum R × PrimeSpectrum R |
                  match (motive := PrimeSpectrum R × PrimeSpectrum R → Prop) x with
                  | (a, b) => a < b})
                q ∧
            RelSeries.last (r :=
                {x : PrimeSpectrum R × PrimeSpectrum R |
                  match (motive := PrimeSpectrum R × PrimeSpectrum R → Prop) x with
                  | (a, b) => a < b})
                p =
              RelSeries.last (r :=
                {x : PrimeSpectrum R × PrimeSpectrum R |
                  match (motive := PrimeSpectrum R × PrimeSpectrum R → Prop) x with
                  | (a, b) => a < b})
                q
p : LTSeries (PrimeSpectrum R)
hx :
  x ∈
    (RelSeries.last (r :=
        {x : PrimeSpectrum R × PrimeSpectrum R |
          match (motive := PrimeSpectrum R × PrimeSpectrum R → Prop) x with
          | (a, b) => a < b})
        p).asIdeal
hp :
  p.length (r :=
      {x : PrimeSpectrum R × PrimeSpectrum R |
        match (motive := PrimeSpectrum R × PrimeSpectrum R → Prop) x with
        | (a, b) => a < b}) =
    n + 1
h0 : n = 0
h1 :
  Eq (α :=
    Fin
      (p.length (r :=
          {x : PrimeSpectrum R × PrimeSpectrum R |
            match (motive := PrimeSpectrum R × PrimeSpectrum R → Prop) x with
            | (a, b) => a < b}) +
        1))
    1
    (Fin.last
      (p.length (r :=
        {x : PrimeSpectrum R × PrimeSpectrum R |
          match (motive := PrimeSpectrum R × PrimeSpectrum R → Prop) x with
          | (a, b) => a < b})))
⊢ x ∈
      (p.toFun (r :=
          {x : PrimeSpectrum R × PrimeSpectrum R |
            match (motive := PrimeSpectrum R × PrimeSpectrum R → Prop) x with
            | (a, b) => a < b})
          1).asIdeal ∧
    n + 1 =
        p.length (r :=
          {x : PrimeSpectrum R × PrimeSpectrum R |
            match (motive := PrimeSpectrum R × PrimeSpectrum R → Prop) x with
            | (a, b) => a < b}) ∧
      RelSeries.head (r :=
            {x : PrimeSpectrum R × PrimeSpectrum R |
              match (motive := PrimeSpectrum R × PrimeSpectrum R → Prop) x with
              | (a, b) => a < b})
            p =
          RelSeries.head (r :=
            {x : PrimeSpectrum R × PrimeSpectrum R |
              match (motive := PrimeSpectrum R × PrimeSpectrum R → Prop) x with
              | (a, b) => a < b})
            p ∧
        RelSeries.last (r :=
            {x : PrimeSpectrum R × PrimeSpectrum R |
              match (motive := PrimeSpectrum R × PrimeSpectrum R → Prop) x with
              | (a, b) => a < b})
            p =
          RelSeries.last (r :=
            {x : PrimeSpectrum R × PrimeSpectrum R |
              match (motive := PrimeSpectrum R × PrimeSpectrum R → Prop) x with
              | (a, b) => a < b})
            p

Tactic:
simpa [h1, hp] using hx