TITLE: If $f,f_m$ are Lipschitz with $\lim_{m\to+\infty} d(f_m(x),f(x)) = 0 $, is it true that the fixed point of $f_m$ converges to the fixed point of $f$?
QUESTION [6 upvotes]: I'm going through a proof in which at one point, the authors make the following statement :

Let $(X,d)$ be a complete metric space and $f:X\to X$ and $f_m:X\to X$ Lipschitz with $lip(f)<1$ and $lip(f_m)<1\; \forall m\in\mathbb{N}$. Let $x^*_m$ the fixed point of $f_m$ and $x^*$ the fixed point of $f$.
If for each  $x\in X$ we have that
$$\lim_{m\to+\infty} d(f_m(x),f(x)) = 0, $$ it follows that $$\lim_{m\to+\infty} d(x^*_m,x^*) = 0 .$$

I tried to figure out how they came up with this by an argument along the lines of
\begin{align*}d(x^*_m,x^*) &= d(f_m(x^*_m),f(x^*)) \leq d(f_m(x^*_m),f(x_m^*))+ d(f(x_m^*),f(x^*))\\&\leq d(f_m(x^*_m),f(x_m^*))+lip(f)d(x_m^*,x^*).
\end{align*}
Then
$$0\leq (1-lip(f))d(f(x_m^*),f(x^*))\leq d(f_m(x^*_m),f(x_m^*)).$$
But now we can't apply the first limit because $x_m^*$  depends on $m$.
Also another thing I tried is by using the fact that $$\lim_{n
\to+\infty}d(f^{\circ n}(x),x^*)=0 \; \forall x\in X$$
Where $f^{\circ n} = \underbrace{f\circ f\circ \dots \circ f}_{\text {n times}}.$
Then for a fixed $x\in X$
\begin{equation*}d(x^*_m,x^*)\leq d(x^*_m,f^{\circ n}_m(x)) + d(f^{\circ n}_m(x),f^{\circ n}(x))+ d(f^{\circ n}(x),x^*),\; \forall n\in\mathbb{N}
\end{equation*}
Now let $\varepsilon > 0$ and set $N$ big enough so that $d(f^{\circ N}(x),x^*)<\varepsilon/3$ and $d(f_m^{\circ N}(x),x_m^*)< \varepsilon/3$.
Then \begin{align*}
d(x^*_m,x^*) &\leq d(x^*_m,f^{\circ N}_m(x)) + d(f^{\circ N}_m(x),f^{\circ N}(x))+ d(f^{\circ N}(x),x^*)\\&<2\varepsilon/3 + d(f^{\circ N}_m(x),f^{\circ N}(x)).
\end{align*}
Now it can be shown that $\lim\limits_{m\to+\infty} d(f^{\circ N}_m(x),f^{\circ N}(x)) =0$, so there is some $M$ such that $d(f^{\circ N}_m(x),f^{\circ N}(x)) <\varepsilon/3\; \forall m>M$, from which we get $$d(x^*_m,x^*)<\varepsilon.$$
But I feel like something is not right in my second attempt.
Is something missing from the statement?

REPLY [2 votes]: If there exists $c\in(0,1)$ such that $lip(f_{n})\leq c$ for all $n$, then it is easy. For, observe that
\begin{eqnarray*}
d(x_{n}^{\ast},x^{\ast}) & = & d(f_{n}(x_{n}^{\ast}),f(x^{\ast}))\\
 & \leq & d(f_{n}(x_{n}^{\ast}),f_{n}(x^{\ast}))+d(f_{n}(x^{\ast}),f(x^{\ast}))\\
 & \leq & lip(f_{n})d(x_{n}^{\ast},x^{\ast})+d(f_{n}(x^{\ast}),f(x^{\ast}))\\
 & \leq & c\cdot d(x_{n}^{\ast},x^{\ast})+d(f_{n}(x^{\ast}),f(x^{\ast}))
\end{eqnarray*}
Therefore, $d(x_{n}^{\ast},x^{\ast})\leq\frac{1}{1-c}\cdot d(f_{n}(x^{\ast}),f(x^{\ast})).$
Letting $n\rightarrow\infty$ and observe that $d(f_{n}(x^{\ast}),f(x^{\ast}))\rightarrow0,$
the result follows.