Missing \(y\) as in \(ay^{\prime \prime \prime }+by^{\prime \prime }+cy^{\prime }=f\left ( x\right ) \)

ode internal name "higher_order_ODE_missing_y"

Since \(y\) is missing, we then assume \(y^{\prime }=u\) and the ode reduces to one order less. Now the lower order ode is solved.