\[ y'(x)-\tan (x y(x))=0 \] ✓ Mathematica : cpu = 0.354255 (sec), leaf count = 69
\[\text {Solve}\left [\frac {1}{2} \sqrt {\frac {\pi }{2}} e^{\frac {x^2}{2}} \left (\text {erfi}\left (\frac {y(x)-i x}{\sqrt {2}}\right )+\text {erfi}\left (\frac {y(x)+i x}{\sqrt {2}}\right )\right )=c_1 e^{\frac {x^2}{2}},y(x)\right ]\] ✓ Maple : cpu = 0.283 (sec), leaf count = 44
\[ \left \{ y \left ( x \right ) =-i{\it RootOf} \left ( -{\it Erf} \left ( {\frac { \left ( -x+{\it \_Z} \right ) \sqrt {2}}{2}} \right ) \sqrt {\pi }-\sqrt {\pi }{\it Erf} \left ( {\frac {\sqrt {2} \left ( x+{\it \_Z} \right ) }{2}} \right ) +\sqrt {2}{\it \_C1} \right ) \right \} \]