3 of 4 method `def a` instead of multiple `u drop 2`

Scala 412 376 349 335:

object P extends Application{
def p(t:List[String],u:List[Double]):Double={
def a=u drop 2
t match{
case Nil=>u.head
case x::y=>x match{
case "+"=>p(y,(u(1)+u(0))::a)
case "-"=>p(y,(u(1)-u(0))::a)
case "*"=>p(y,(u(1)*u(0))::a)
case "/"=>p(y,(u(1)/u(0))::a)
case d=>p(y,d.toDouble::u)}}}
println (p((readLine() split " ").toList,Nil))}