Duplieren is the term for a second cut performed behind the blade of the opponent, having first met them with a preceding strike.
It is a response to a STRONG parry/bind.
The typical interpretation is seen in the application below, with a mirror of it being applied from the left side.
|Vom tag, left leg forward||Vom tag, left leg forward, at measure|
|Cut an Oberhau to the upper left opening with a Passing Step of the right foot||At once cut an Oberhauw to the upper left opening in the same way.|
|Parry strongly with the blade||Act Indes, remaining Strong(1) on the sword, driving up with the arms and pushing the pommel under the right arm, cutting(2) behind their blade to the head with the long edge.|
(1) Whether the usage of "Strong" here refers to the Strong of the blade, or to an act of remaining physically strong in the bind is unclear, as the two are often used throughout the text. Experimentation shows that the former is essential in protecting the head.
(2) The type of cut is not specified, though effectively any cut with high hands and the long edge will suffice. This means cuts like a Zwerchau or high Krumphau behind their blade are quite effective.
It is also not clear how long we should remain on the opponent's blade for, however the Trosclair traslation from Ringeck specifying:
" strike him through the maw, with crossed hands, upon the sword behind his sword's blade (between the sword and the man)"
Implies that there is a remaining on the blade through the movement, which experiment shows assists in protecting against reprisals from the opponent by keeping their blade on the strong of our own, and kept safe by our crossguard.
Finally we notice that in the example application given (based on the von Danzig description) the movement is an action in response to an incoming cut. The Ringeck gloss makes it clear that the technique can also be used when you are acting in the Vor, cutting with an Oberhau in first intention.
Rendered as Doplieren in Meyer, and often interpreted as being performed in a slightly different way.