\[ y(x) y''(x)-y'(x)^2-1=0 \] ✓ Mathematica : cpu = 0.169659 (sec), leaf count = 80
\[\left \{\left \{y(x)\to -\frac {e^{-c_1} \tanh \left (e^{c_1} (c_2+x)\right )}{\sqrt {\tanh ^2\left (e^{c_1} (c_2+x)\right )-1}}\right \},\left \{y(x)\to \frac {e^{-c_1} \tanh \left (e^{c_1} (c_2+x)\right )}{\sqrt {\tanh ^2\left (e^{c_1} (c_2+x)\right )-1}}\right \}\right \}\] ✓ Maple : cpu = 0.211 (sec), leaf count = 42
\[ \left \{ y \left ( x \right ) ={\frac {{\it \_C1}}{2} \left ( \left ( {{\rm e}^{{\frac {{\it \_C2}}{{\it \_C1}}}}} \right ) ^{2} \left ( {{\rm e}^{{\frac {x}{{\it \_C1}}}}} \right ) ^{2}+1 \right ) \left ( {{\rm e}^{{\frac {{\it \_C2}}{{\it \_C1}}}}} \right ) ^{-1} \left ( {{\rm e}^{{\frac {x}{{\it \_C1}}}}} \right ) ^{-1}} \right \} \]