5.2.2 Missing \(y\)

ode internal name "higher_order_ODE_missing_y"

This works for linear and non-linear ode. Since \(y\) is missing, we then assume \(y^{\prime }=u,y^{\prime \prime }=u^{\prime },y^{\prime \prime \prime }=u^{\prime \prime }\) and so on. The ode reduces to one order less. Now the lower order ode is solved. Note if the higher order ode is missing both \(x\) and \(y\) at same time, then this substitution and the above one also work.