$3\mathrm{.}40)$ that one can write a relativistic equation for a massless $2-$component fermion field that transforms as the upper two components of a Dirac spinor $($UL$).$ Call such a $2-$component field Xa$($x$),$ a $==1,2.($a$)$ Show that it is possible to write an equation for x$($x$)$ as a massive field in the following way: io$.2$x imo$2$x$*=0.$ That is$,$ show, first, that this equation is