To establish duality only requires establishing theorems which are the dual versions of the axioms for the dimension in question.
It can now be found in dual flush versions.
A dual version of this gives the Poincaré lemma.
The first two of them are dual versions (series and parallel) of the general positive feedback system.
A "dual" version of the Principle: "there is at least one person such that if anybody drinks, then he does."
Nokia has disclosed its first dual versions of X Series mobile phone.
In 1989 a dual English-Albanian version was published.
The Commodore 1572 was a dual version of the Commodore 1571 single disk drive.
The dual version is called 556.
This is the dual version of the inverse of a quaternion.