sp {elaborate*shields-on
   (state <s> ^operator.actions <a>
              ^io.input-link <il>)
   (<il> ^incoming.<dir> yes
         ^shield-status off)
   -->
   (<a> ^shields.switch on)}

sp {elaborate*shields-off
   (state <s> ^operator.actions <a>
              ^io.input-link <il>)
   (<il> -^incoming.<dir> yes
          ^shield-status on)
   --> 
   (<a> ^shields.switch off)}

