This is a simplified version of the BirthdayBook example in Z represented in Z Markup Language.
NAME
DATE
BirthdayBook
known
pset
NAME
birthday
NAME
pfun
DATE
known
=
dom
birthday
InitBirthdayBook
BirthdayBook
known
=
emptyset
AddBirthday
BirthdayBook
name?
NAME
date?
DATE
name?
nem
known
birthday
'
=
birthday
uni
{
(
name?
,
date?
)
}
RemoveBirthday
BirthdayBook
name?!
NAME
name?
mem
known
birthday
'
=
{
name?
}
dsub
birthday
FindBirthday
BirthdayBook
name?
NAME
date!
DATE
name?
mem
known
(
name?
,
date!
)
mem
birthday