✓ Mathematica : cpu = 0.0205026 (sec), leaf count = 31
DSolve[{-x[t] + t*Derivative[1][x][t] + a*Derivative[1][y][t] + Derivative[1][y][t]^2 == 0, -y[t] + t*Derivative[1][y][t] + Derivative[1][x][t]*Derivative[1][y][t] == 0},{x[t], y[t]},t]
✓ Maple : cpu = 0.314 (sec), leaf count = 144
dsolve({diff(x(t),t)*diff(y(t),t)+t*diff(y(t),t)-y(t) = 0, diff(x(t),t)^2+t*diff(x(t),t)+a*diff(y(t),t)-x(t) = 0})