def last(n = nil)
      require_terminating_rules
      occurrences = enumerate_occurrences(start_time).to_a
      n.nil? ? occurrences.last : occurrences[-n..-1]
    end
def last(n = nil)
      require_terminating_rules
      occurrences = enumerate_occurrences(start_time).to_a
      n.nil? ? occurrences.last : occurrences[-n..-1]
    end
Get the final n occurrences of a terminating schedule
 or the final one if no n is given