at $T=0$ and at $k=k_{F}$ one has $(A_{2}/A_{1})\sim0.1$. From this analysis we conclude that the ARPES measurements at $k_{F}$ should give the similar ratio as at $k=0$. The calculated $ARPES$ spectra at $T=0$ $K$ and at $k=k_{F}$ give $\Delta
\omega=\left\vert \omega_{2}-\omega_{1}\right\vert =\Omega\sqrt{1+\lambda_{m}}$ while the experimental value is $\Delta\omega\approx100$ $meV$, which for $\lambda_{m}^{(ARPES)}\approx0.2$ gives the optical phonon energy of the order of $\Omega\approx90$ $meV$.

The superconducting critical temperature $T_{c0}$ and gap $\Delta
_{0}$
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In the weak coupling limit ($\lambda_{m}\ll1$) of the Eliashberg equations with $q_{c}v_{F}<\pi T_{c0}$ ($v_{F}$ is the Fermi velocity) the linearized gap equation (near $T_{c0}$) is given by $$\Delta(\mathbf{k},\omega_{n})=T_{c0}\sum_{\mathbf{q}}\sum_{m}\frac
{V_{epi}(q,\omega_{n}-\omega_{m})\Delta(\mathbf{k}+\mathbf{q},\omega_{m})}{\omega_{m}^{2}+\xi^{2}(\mathbf{k}+\mathbf{q})}, \label{Delta}$$ where $\omega_{n}=\pi T_{c0}(2n+1)$, $V_{epi}(\mathbf{q},\Omega_{n})=g_{epi}^{2}(\mathbf{q})(2\Omega/(\Omega_{n}^{2}+\Omega^{2}))$, $\Omega
_{n}=2\pi T_{c0}\cdot n$. For $\Omega\gg\pi T_{c0}$ one has $V_{epi}(\mathbf{q},\Omega_{n})\approx V_{epi}(\mathbf{q},0)=2g_{epi}^{2}(\mathbf{q})/\hbar\Omega$. In the strong $FSP$ limit when $(q_{c}v_{F})\ll(\pi
T_{c0})^{2}$ the highest value of $\Delta(\mathbf{k},\omega_{n})$ is reached at $\mathbf{k}=\mathbf{k}_{F}$ ($\xi(\mathbf{k}_{F})=0$ in $Eq.$(\[Delta\]). The solution $\Delta(\mathbf{k},\omega_{n})$ is searched in the standard BCS-like *square-well* approximation $\Delta(\mathbf{k}_{F},\omega
_{n})\approx\Delta_{0}=const$. In leading order with respect to $(T_{c0}/\Omega)\ll1$ one obtains $T_{c0}$ [@Kulic-PhysRep]-[@Dan-Dol-Kul-Oud] $$T_{c0}\approx\frac{1}{\pi^{2}}\left\langle V_{epi}(\mathbf{q})\right\rangle
_{q}\sum_{-\Omega/\pi T_{c0}}^{\Omega/\pi T_{c0}}\frac{1}{(2m+1)^{2}}
\label{Tco}$$ For $\Omega\gg\pi T_{c0}$ this gives $T_{c0}=\left\langle V_{epi}(\mathbf{q})\right\rangle _{q}/4\approx(1/16\pi)(aq_{c})^{2}(2g_{0}^{2}/\Omega)$, where $a$ is the $Fe-Fe$ distance. Note, that $T_{c0}$ is *mass-independent (*$\alpha_{O}=0$) - note $\alpha_{O}=1/2$ is found in [@Johnston1-2]. The small isotope-effect can be 