\[ y^{(3)}(x)+y(x) y''(x)-y'(x)^2+1=0 \] ✗ Mathematica : cpu = 0.034647 (sec), leaf count = 0 , could not solve
DSolve[1 - Derivative[1][y][x]^2 + y[x]*Derivative[2][y][x] + Derivative[3][y][x] == 0, y[x], x]
✓ Maple : cpu = 0.816 (sec), leaf count = 73
\[\left \{y \left (x \right ) = \mathit {ODESolStruc} \left (\textit {\_a} , \left [\left \{\textit {\_a} \textit {\_}b\left (\textit {\_a} \right ) \left (\frac {d}{d \textit {\_a}}\mathrm {\_}\mathrm {b}\left (\textit {\_a} \right )\right )+\textit {\_}b\left (\textit {\_a} \right )^{2} \left (\frac {d^{2}}{d \textit {\_a}^{2}}\mathrm {\_}\mathrm {b}\left (\textit {\_a} \right )\right )+\textit {\_}b\left (\textit {\_a} \right ) \left (\frac {d}{d \textit {\_a}}\mathrm {\_}\mathrm {b}\left (\textit {\_a} \right )\right )^{2}-\textit {\_}b\left (\textit {\_a} \right )^{2}+1=0\right \}, \left \{\textit {\_a} =y \left (x \right ), \textit {\_}b\left (\textit {\_a} \right )=\frac {d}{d x}y \left (x \right )\right \}, \left \{x =c_{1}+\int \frac {1}{\textit {\_}b\left (\textit {\_a} \right )}d \textit {\_a} , y \left (x \right )=\textit {\_a} \right \}\right ]\right )\right \}\]