Cleaner (shorter) way to write this?

sieve.rb

def can_delete? (object)
  r_val = false
  r_val = can_delete_by_core_role? object
  unless r_val
    r_val = can_delete_by_owner? object
    unless r_val
      r_val = can_delete_by_zone_role? object
      unless r_val
        r_val = can_delete_by_access_profile? object
      end
    end
  end
  return r_val
end