(defrule init
	(true null)
=>
	(add (gives-milk animal))
	(add (has-hoofs animal))
	(delete (true null))
)

(defrule bird-test
	(has-feathers ?)
=>
	(bird ?)
)

(defrule mammal-test
	(gives-milk ?)
=>
	(add (mammal ?))
)

(defrule ungulate-test1
	(mammal ?)
	(chews-cud ?)
=>
	(add (is-ungulate ?))
)

(defrule ungulate-test2
	(mammal ?)
	(has-hoofs ?)
=>
	(add (is-ungulate ?)
)