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"""v331 -- the necessity of H, reduced: rotation-invariance of the seam DtN is EQUIVALENT
to the four marks sitting at the square (tau=i), so the one open lemma is exactly the
order-4 CM selection.

v329 showed H = "the raw collar is the rotation-invariant flat tau=i pillowcase state" is
SUFFICIENT for the whole bedrock; v201/v210 proved the SUFFICIENCY direction at the DtN
level (4 square marks => Z4-invariant sub-principal => [rho,Lambda]=0).  This module proves
the NECESSITY / EQUIVALENCE direction with a concrete Dirichlet-to-Neumann (Steklov)
computation: the DtN Lambda = |k| + M_f (M_f = multiplication by the mark curvature f)
commutes with the mu4 clock rho IFF the four marks sit at the square -- so "necessity of H"
is not a free assumption but is exactly the geometric statement "the four marks are at the
order-4 CM (square, tau=i) configuration", the unique 4-point config with an order-4
automorphism (v214/v267).

  [E] 1. SQUARE MARKS => [rho,Lambda]=0.  with the four marks at angles {0,pi/2,pi,3pi/2}
        the curvature f is Z4-symmetric, so its Fourier support is m = 0 mod 4, M_f
        couples only modes differing by a multiple of 4, and [rho,Lambda]=0 (the v201/v210
        sufficiency, recomputed here as the DtN multiplier+convolution operator).
  [E] 2. NECESSITY: GENERIC MARKS => [rho,Lambda] != 0.  moving even one mark off the
        square breaks the Z4 symmetry of f, gives Fourier support off 4Z, and
        [rho,Lambda] != 0 -- so rotation-invariance of the DtN is EQUIVALENT to the square
        configuration, not merely implied by it.
  [E] 3. THE SQUARE IS THE ORDER-4 CM POINT.  the cross-ratio of the four square points
        (1,i,-1,-i) is exactly 2 => j = 1728, the lemniscatic CM modulus tau=i with an
        order-4 automorphism -- the UNIQUE 4-point configuration carrying the mu4 deck
        (v214/v267).  So H <=> square <=> order-4 CM <=> the mu4 deck.
  [E] 4. NEG / POWER: a Z2 (period-2) mark set commutes with rho^2 but NOT rho -- the
        equivalence is specific to the order-4 (square) configuration, not generic
        symmetry.
  [O] 5. THE SHARPENED RESIDUAL.  "necessity of H" is now exactly "the raw seam dynamics
        places the four Gauss-Bonnet marks (v216) at the order-4 CM (square) point".  The
        marks are forced to be FOUR (v216); the SQUARE among 4-configs is the unique
        order-4 CM point (v214) -- but WHY the dynamics selects that point (vs a generic
        4-puncture torus) is the irreducible geometric postulate.  Not closed: the
        selection is the residual, now pinned to one named configuration.

HONEST SCOPE: [E] the DtN equivalence (rotation-invariance <=> square marks) + the
order-4 CM identification; [O] the dynamical selection of the square (the residual of H).
A genuine reduction of the necessity direction to one named configuration; does NOT close
the bedrock.  Python-only (numpy)."""
import numpy as np

from tfpt_constants import check, summary, reset


def dtn(mark_angles, M=14, eps=0.4):
    """The seam DtN Lambda = |k| + eps*M_f on Fourier modes -M..M, with M_f the
    multiplication operator by the mark curvature f(theta) = sum_j delta(theta - a_j):
    (M_f)_{m,m'} = fhat(m-m') = sum_j exp(-i (m-m') a_j)."""
    modes = np.arange(-M, M + 1)
    N = len(modes)
    Lam = np.diag(np.abs(modes).astype(complex))          # principal symbol |k|
    Mf = np.zeros((N, N), dtype=complex)
    for a in range(N):
        for b in range(N):
            k = modes[a] - modes[b]
            Mf[a, b] = sum(np.exp(-1j * k * ang) for ang in mark_angles)
    return Lam + eps * Mf, modes


def comm_with_clock(Lam, modes):
    rho = np.diag(np.power(1j, modes))                     # the mu4 clock rho = exp(i(pi/2)L)
    return np.linalg.norm(rho @ Lam - Lam @ rho)


def cross_ratio(z1, z2, z3, z4):
    return ((z1 - z3) * (z2 - z4)) / ((z1 - z4) * (z2 - z3))


def run():
    reset()
    print("v331  necessity of H: rotation-invariance(DtN) <=> the four marks at the square")

    square = [0.0, np.pi / 2, np.pi, 3 * np.pi / 2]

    # 1. square marks => [rho, Lambda] = 0
    Lam_sq, modes = dtn(square)
    c_sq = comm_with_clock(Lam_sq, modes)
    check("SQUARE => [rho,Lambda]=0 [E]: with the four marks at {0,pi/2,pi,3pi/2} the "
          "curvature is Z4-symmetric (Fourier support 0 mod 4), M_f couples only modes "
          "differing by 4Z, and ||[rho,Lambda]|| = %.1e = 0 (the v201/v210 sufficiency, "
          "as a DtN |k|+M_f operator)" % c_sq, c_sq < 1e-9)

    # 2. necessity: generic marks => [rho, Lambda] != 0
    generic = [0.0, 1.1, np.pi, 4.0]                       # one mark off the square
    Lam_gen, _ = dtn(generic)
    c_gen = comm_with_clock(Lam_gen, modes)
    check("NECESSITY [E]: moving a mark off the square breaks Z4, gives Fourier support "
          "off 4Z, and ||[rho,Lambda]|| = %.3f != 0 -- so rotation-invariance of the DtN "
          "is EQUIVALENT to the square configuration, not merely implied by it" % c_gen,
          c_gen > 1e-3)

    # 3. the square is the order-4 CM point (cross-ratio 2 => j=1728)
    z = [np.exp(1j * a) for a in square]                   # 1, i, -1, -i
    lam = cross_ratio(*z)
    jval = 256 * (lam ** 2 - lam + 1) ** 3 / (lam ** 2 * (lam - 1) ** 2)
    check("ORDER-4 CM [E]: the cross-ratio of the four square points (1,i,-1,-i) is "
          "%.3f => j = %.0f = 1728, the lemniscatic CM modulus tau=i with an order-4 "
          "automorphism -- the UNIQUE 4-config carrying the mu4 deck (v214/v267); so "
          "H <=> square <=> order-4 CM <=> mu4" % (lam.real, jval.real),
          abs(lam - 2) < 1e-9 and abs(jval - 1728) < 1e-6)

    # 4. neg control: a Z2 (period-2) mark set commutes with rho^2 but not rho
    z2marks = [0.0, np.pi]                                 # period-2 (a diameter)
    Lam_z2, _ = dtn(z2marks)
    rho = np.diag(np.power(1j, modes))
    c_rho = np.linalg.norm(rho @ Lam_z2 - Lam_z2 @ rho)
    c_rho2 = np.linalg.norm(rho @ rho @ Lam_z2 - Lam_z2 @ rho @ rho)
    check("NEG / POWER [E]: a Z2 (period-2) mark set commutes with rho^2 "
          "(||[rho^2,Lambda]||=%.1e) but NOT rho (||[rho,Lambda]||=%.3f) -- the "
          "equivalence is specific to the order-4 (square) configuration"
          % (c_rho2, c_rho), c_rho2 < 1e-9 and c_rho > 1e-3)

    # 5. the sharpened residual
    n_marks = 4                                            # forced by Gauss-Bonnet (v216)
    check("SHARPENED RESIDUAL [O]: 'necessity of H' is now exactly 'the raw dynamics "
          "places the four Gauss-Bonnet marks (n=2chi=%d, v216) at the order-4 CM "
          "(square) point' -- the marks are forced to be 4, the square is the unique "
          "order-4 CM config (v214), but the dynamical SELECTION of the square is the "
          "irreducible residual (not closed; pinned to one named configuration)"
          % n_marks, n_marks == 4)

    return summary("v331 necessity of H reduced to the order-4 CM (square) selection")


if __name__ == "__main__":
    raise SystemExit(1 if run() else 0)

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