\[ y(x) y''(x)-y'(x)^2+1=0 \] ✓ Mathematica : cpu = 0.0764722 (sec), leaf count = 44
\[\left \{\left \{y(x)\to -e^{-c_1} \sinh \left (e^{c_1} \left (c_2+x\right )\right )\right \},\left \{y(x)\to e^{-c_1} \sinh \left (e^{c_1} \left (c_2+x\right )\right )\right \}\right \}\]
✓ Maple : cpu = 0.329 (sec), leaf count = 79
\[ \left \{ y \left ( x \right ) ={\frac {{\it \_C1}}{2} \left ( {1 \left ( {{\rm e}^{{\frac {{\it \_C2}}{{\it \_C1}}}}} \right ) ^{-2} \left ( {{\rm e}^{{\frac {x}{{\it \_C1}}}}} \right ) ^{-2}}-1 \right ) {{\rm e}^{{\frac {{\it \_C2}}{{\it \_C1}}}}}{{\rm e}^{{\frac {x}{{\it \_C1}}}}}},y \left ( x \right ) ={\frac {{\it \_C1}}{2} \left ( \left ( {{\rm e}^{{\frac {{\it \_C2}}{{\it \_C1}}}}} \right ) ^{2} \left ( {{\rm e}^{{\frac {x}{{\it \_C1}}}}} \right ) ^{2}-1 \right ) \left ( {{\rm e}^{{\frac {{\it \_C2}}{{\it \_C1}}}}} \right ) ^{-1} \left ( {{\rm e}^{{\frac {x}{{\it \_C1}}}}} \right ) ^{-1}} \right \} \]