$\mathbb{N}$
0$\leq$s<k⇒g$_{k}$($a_{s}$)=0
$b_k$=$\sum_{m=0}^{k}$$c_k(m)$f($a_m$)
$c_a(b)$=$\sum_{k=1}^{a}$$(-1)^{k}$$\sum_{L_{k,0} \lt L_{k,1}… \lt L_{k,k} }^{L_{k,0}=b,L_{k,k}=a+b}$$\frac{ \prod_{I=0}^{k-1}g_{L_{k,I}}(a_{L_{k,I+1}}) }{ \prod_{I=0}^{k}g_{L_{k,I}}(a_{L_{k,I}}) }$
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