(a) kernel of D_f*E in the k_x=0 block for eps*c in 4 pi Z (large c): 4 smallest |lam| vs truncation |k_y|<=K
  eps=+2.50 c=  +5.0265 eps*c/(4pi)=+1.000:  K=20: 1.4e-13 | next 6.61;  K=40: 1.8e-13 | next 6.61;  K=80: 1.0e-12 | next 6.61
  eps=+1.00 c= +12.5664 eps*c/(4pi)=+1.000:  K=20: 8.5e-14 | next 6.34;  K=40: 3.7e-13 | next 6.34;  K=80: 5.9e-13 | next 6.34
  eps=-1.00 c= +25.1327 eps*c/(4pi)=-2.000:  K=20: 1.6e-13 | next 6.34;  K=40: 4.5e-13 | next 6.34;  K=80: 3.8e-13 | next 6.34
  eps=+3.00 c=  +4.1888 eps*c/(4pi)=+1.000:  K=20: 1.0e-13 | next 6.74;  K=40: 3.2e-13 | next 6.74;  K=80: 9.5e-13 | next 6.74
  eps=+0.10 c=+125.6637 eps*c/(4pi)=+1.000:  K=20: 1.3e-13 | next 6.28;  K=40: 2.3e-13 | next 6.28;  K=80: 3.7e-13 | next 6.28
  eps=+0.25 c= -50.2655 eps*c/(4pi)=-1.000:  K=20: 4.8e-14 | next 6.29;  K=40: 3.0e-13 | next 6.29;  K=80: 4.0e-13 | next 6.29

(b) number of eigenvalues of Delta_0, Delta_1, Delta_2 in [0,1] (k_x=0 block contains all eigenvalues < 4 pi^2 - O(r));
    also the lowest eigenvalue of Delta_0; r = |eps|(1+c^2)^(1/2)
  c=0.5 eps=0.25 r=0.280:  E: [1, 2, 1] (min Delta_0 = 0.0312);  fE: [1, 2, 1] (min Delta_0 = 0.0352)
  c=0.5 eps=0.50 r=0.559:  E: [1, 2, 1] (min Delta_0 = 0.1250);  fE: [1, 2, 1] (min Delta_0 = 0.1406)
  c=0.5 eps=1.00 r=1.118:  E: [1, 2, 1] (min Delta_0 = 0.4992);  fE: [1, 2, 1] (min Delta_0 = 0.5617)
  c=0.5 eps=1.25 r=1.398:  E: [1, 2, 1] (min Delta_0 = 0.7793);  fE: [1, 2, 1] (min Delta_0 = 0.8770)
  c=0.5 eps=1.40 r=1.565:  E: [1, 2, 1] (min Delta_0 = 0.9770);  fE: [0, 2, 0] (min Delta_0 = 1.0994)
  c=0.5 eps=1.50 r=1.677:  E: [0, 2, 0] (min Delta_0 = 1.1210);  fE: [0, 2, 0] (min Delta_0 = 1.2616)
  c=0.5 eps=2.00 r=2.236:  E: [0, 2, 0] (min Delta_0 = 1.9873);  fE: [0, 2, 0] (min Delta_0 = 2.2373)
  c=1.0 eps=0.25 r=0.354:  E: [1, 2, 1] (min Delta_0 = 0.0312);  fE: [1, 2, 1] (min Delta_0 = 0.0469)
  c=1.0 eps=0.50 r=0.707:  E: [1, 2, 1] (min Delta_0 = 0.1250);  fE: [1, 2, 1] (min Delta_0 = 0.1875)
  c=1.0 eps=1.00 r=1.414:  E: [1, 2, 1] (min Delta_0 = 0.4992);  fE: [1, 2, 1] (min Delta_0 = 0.7492)
  c=1.0 eps=1.25 r=1.768:  E: [1, 2, 1] (min Delta_0 = 0.7793);  fE: [0, 2, 0] (min Delta_0 = 1.1699)
  c=1.0 eps=1.40 r=1.980:  E: [1, 2, 1] (min Delta_0 = 0.9770);  fE: [0, 2, 0] (min Delta_0 = 1.4669)
  c=1.0 eps=1.50 r=2.121:  E: [0, 2, 0] (min Delta_0 = 1.1210);  fE: [0, 2, 0] (min Delta_0 = 1.6834)
  c=1.0 eps=2.00 r=2.828:  E: [0, 2, 0] (min Delta_0 = 1.9873);  fE: [0, 2, 0] (min Delta_0 = 2.9870)
  c=2.0 eps=0.25 r=0.559:  E: [1, 2, 1] (min Delta_0 = 0.0312);  fE: [1, 2, 1] (min Delta_0 = 0.0937)
  c=2.0 eps=0.50 r=1.118:  E: [1, 2, 1] (min Delta_0 = 0.1250);  fE: [1, 2, 1] (min Delta_0 = 0.3750)
  c=2.0 eps=1.00 r=2.236:  E: [1, 2, 1] (min Delta_0 = 0.4992);  fE: [0, 2, 0] (min Delta_0 = 1.4992)
  c=2.0 eps=1.25 r=2.795:  E: [1, 2, 1] (min Delta_0 = 0.7793);  fE: [0, 0, 0] (min Delta_0 = 2.3417)
  c=2.0 eps=1.40 r=3.130:  E: [1, 2, 1] (min Delta_0 = 0.9770);  fE: [0, 0, 0] (min Delta_0 = 2.9368)
  c=2.0 eps=1.50 r=3.354 (r>=pi):  E: [0, 2, 0] (min Delta_0 = 1.1210);  fE: [0, 0, 0] (min Delta_0 = 3.3708)
  c=2.0 eps=2.00 r=4.472 (r>=pi):  E: [0, 2, 0] (min Delta_0 = 1.9873);  fE: [0, 0, 0] (min Delta_0 = 5.9859)

(c) counting functions N(lam) = #{eigs in [-lam, lam]} for eps=0.3, c=2 (k_x in -2..2 blocks)
   E: N(0)=0, N(1e-10)=4, N(0.2)=4, N(0.299)=4, N(0.3)=4, N(0.5)=4, N(1)=4, N(3)=4, N(5.5)=4, N(5.61)=4, N(6.3)=20
  fE: N(0)=0, N(1e-10)=0, N(0.2)=0, N(0.299)=0, N(0.3)=4, N(0.5)=4, N(1)=4, N(3)=4, N(5.5)=4, N(5.61)=4, N(6.3)=16
  r = 0.6708, 2pi - r = 5.6124, |eps c|/2 = 0.3000, (|c|/4pi)*||F|| = 0.3000
