\[ \left \{x'(t)+y'(t)+y(t)=f(t),x''(t)+x(t)+y''(t)+y'(t)+y(t)=g(t)\right \} \] ✓ Mathematica : cpu = 0.008374 (sec), leaf count = 44
\[\left \{\left \{x(t)\to -f''(t)-f'(t)-f(t)+g'(t)+g(t),y(t)\to f''(t)+f(t)-g'(t)\right \}\right \}\] ✓ Maple : cpu = 0.036 (sec), leaf count = 48
\[\{x \relax (t ) = -\frac {d}{d t}f \relax (t )+g \relax (t )-f \relax (t )-\frac {d^{2}}{d t^{2}}f \relax (t )+\frac {d}{d t}g \relax (t ), y \relax (t ) = f \relax (t )+\frac {d^{2}}{d t^{2}}f \relax (t )-\frac {d}{d t}g \relax (t )\}\]