The equation $t y^{\prime \prime \prime}+(1-t) y^{\prime \prime}+t y^{\prime}-y=0$
has $f(t)=t$ as a solution. Use the substitution $y(t)=$ $v(t) f(t)$ to reduce this third-order equation to a homogeneous linear second-order equation in the variable $w=v^{\prime} .$