<= // assign

<| // iterate

within {..} < and > are normal infix comparators.

Person p <| persons
{p.age > 20}
boolean b <= {p.age > 20}
Pet pet <= /p/pets{name == rover}/
Pet pet <| {persons.pets}
String name <= p.name
{pet.name == "rover"}

use the "LHS" in the RHS:

rule x when /* empty */ then {
  List list <= { new ArrayList() }
  sub(
      int i <| { [1, 2, 3, 4, 5, 6] }
      Invader invader <= { invader = new Invader();
                           invader.width = conf.invader1Width;
                           invader.height = conf.invader1Height;
                           invader.speed = conf.invader1Speed;
                           invader.x = 90 * i;
                           invader.y = 40 + conf.invader1Height;
                           invader; )
      { list.add( invader ); }
      { insert( invader ) ); }
  )
  { insert( list ) }
}