This is the reference page to group and synchronize descriptions of xd4. The root document is a pdf and this is xd4 in one view:
x4: A timer and alarm that rings from july 1st 2020 until June 2028.
xd: System theories according to their cognitive availability (amount and complexity of required background knowledge or skills) into structures and classes of structures to form ordering hierarchy [domains d]
xd4.dev: eventually producing a literature outline and efficient line of thought (step wise exploration of formulaeic and co space of the system).