class Top

	def sum as int
		is virtual
		return 1

	def product as int
		return 2

class Bottom
	inherits Top

	def sum as int
		is override
		return base.sum + 2

	def product as int is override
		return base.product * 3

	def main
		is shared
		b as Bottom = Bottom()
		assert b.sum==3
		assert b.product==6