Question 13
Find all functions $f: \mathbb{R}^{+} \rightarrow \mathbb{R}^{+}$ such that
$$
f(x+f(y+x y))=(y+1) f(x+1)-1
$$
for all $x, y \in \mathbb{R}^{+}$.
($\mathbb{R}^{+}$ denotes the set of positive real numbers.)
$$
f(x+f(y+x y))=(y+1) f(x+1)-1
$$
for all $x, y \in \mathbb{R}^{+}$.
($\mathbb{R}^{+}$ denotes the set of positive real numbers.)