\[ y'(x)-e^{x-y(x)}+e^x=0 \] ✓ Mathematica : cpu = 0.0407967 (sec), leaf count = 18
\[\left \{\left \{y(x)\to \log \left (e^{c_1-e^x}+1\right )\right \}\right \}\]
✓ Maple : cpu = 0.135 (sec), leaf count = 20
\[ \left \{ y \left ( x \right ) =-{{\rm e}^{x}}+\ln \left ( -1+{{\rm e}^{{{\rm e}^{x}}+{\it \_C1}}} \right ) -{\it \_C1} \right \} \]