(A) periodic discriminants: tr = x (2-periodic), tr = x^2-2-lam^2 = D_NS(E) (4-periodic): exact on 6x4 grid: True
(B) c^2 - (lam^2+4) = lam^4/16 on the same grid: True
(C) six bands nondegenerate, ordered, equal to the x-description, edges = NS formulas: True
    lam=3.0: bands [-1.3028, -1.1926], [-1.0000, 0.0000], [0.3820, 0.6972], [2.3028, 2.6180], [3.0000, 4.0000], [4.1926, 4.3028]
    lam=5.0: bands [-1.1926, -1.1401], [-0.7016, 0.0000], [0.6972, 0.8074], [4.1926, 4.3028], [5.0000, 5.7016], [6.1401, 6.1926]
(D) Delta + L(delta_0+delta_1): eigenvalue L-1+1/(L-1) in (2,L), exact for L in {21/10,5/2,3,7,12}: True
(E) domain wall: s = -lam delta_{-1}; Delta + mu delta_0 has eigenvalue sign(mu) sqrt(mu^2+4), exact: True
(F) finite domain wall, lam=3.0, 600 sites: E-: dist 8.9e-16, E+: dist 3.0e-01, exactly one: True; G-: dist 6.4e-15, G+: dist 7.0e-01, exactly one: True
(F) finite domain wall, lam=5.0, 600 sites: E-: dist 4.4e-16, E+: dist 4.9e-01, exactly one: True; G-: dist 2.4e-15, G+: dist 8.1e-01, exactly one: True
(F) finite domain wall, lam=-3.0, 600 sites: E-: dist 3.0e-01, E+: dist 8.9e-16, exactly one: True; G-: dist 7.0e-01, G+: dist 6.4e-15, exactly one: True
RESULT: all checks passed
