Given,
$\frac{1}{1 + a + b^{-1}} + \frac{1}{1 + b + c^{-1}} + \frac{1}{1 + c + a^{-1}} = 1$
Solving L.H.S :
$$\begin{aligned}\Rightarrow \frac{1}{1 + a + b^{-1}} + \frac{1}{1 + b + c^{-1}} + \frac{1}{1 + c + a^{-1}} \\[1em] \Rightarrow \frac{1}{1 + a + \frac{1}{b}} + \frac{1}{1 + b + \frac{1}{c}} + \frac{1}{1 + c + \frac{1}{a}}\end{aligned}$$
Multiplying numerator and denominator of first term by b, second term by c, and third term by a we get,
$$\begin{aligned}\Rightarrow \frac{1 \times b}{\Big(1 + a + \frac{1}{b}\Big) \times b} + \frac{1 \times c}{\Big(1 + b + \frac{1}{c}\Big) \times c} + \frac{1 \times a}{\Big(1 + c + \frac{1}{a}\Big) \times a} \\[1em] \Rightarrow \frac{b}{(b + ab + 1)} + \frac{c}{(c + bc + 1)} + \frac{a}{(a + ac + 1)}\end{aligned}$$
Since abc = 1, c = $\frac{1}{ab}$.
Substituting, c = $\frac{1}{ab}$, we get :
$$\begin{aligned}\Rightarrow \frac{b}{(b + ab + 1)} + \frac{\frac{1}{ab}}{\Big(\frac{1}{ab} + b \Big(\frac{1}{ab}\Big) + 1\Big)} + \frac{a}{(a + a \Big(\frac{1}{ab}\Big) + 1)} \\[1em] \Rightarrow \frac{b}{(b + ab + 1)} + \frac{\frac{1}{ab}}{\Big(\frac{1}{ab} + \frac{1}{a} + 1\Big)} + \frac{a}{\Big(a + \frac{1}{b} + 1\Big)} \\[1em] \Rightarrow \frac{b}{(b + ab + 1)} + \frac{1}{ab \times \Big(\frac{1 + b + ab}{ab}\Big)} + \frac{a}{\Big(\frac{ab + 1 + b}{b}\Big)} \\[1em] \Rightarrow \frac{b}{(b + ab + 1)} + \frac{1}{\Big({1 + b + ab}\Big)} + \frac{ab}{\Big(ab + 1 + b\Big)} \\[1em] \Rightarrow \frac{b + 1 + ab}{(b + ab + 1)} \\[1em] \Rightarrow \frac{1 + b + ab}{(1 + b + ab)} \\[1em] \Rightarrow 1.\end{aligned}$$
Hence proved, $\frac{1}{1 + a + b^{-1}} + \frac{1}{1 + b + c^{-1}} + \frac{1}{1 + c + a^{-1}} = 1$.