sp {retreat*propose*move
   (state <s> ^name retreat
              ^direction <dir>
              ^superstate.side-direction.<dir> <ndir>
             -^direction <ndir>
             -^avoid-direction <ndir>
              ^io.input-link.blocked.<ndir> no)
   -->
   (<s> ^operator <o> + =)
   (<o> ^name move
        ^actions.move.direction <ndir>)}
