The phrase "are henceforth" is correct and usable in written English.
It is typically used to indicate that something will be the case from this point forward.
Example: "All employees are henceforth required to submit their reports by Friday."
Alternatives: "will now be" or "are now".
"All ongoing government projects on technical and economic cooperation between the two countries are henceforth suspended," said an official letter to the Cambodian ambassador, who was also expelled.
"The pronouncement by Agha ["sir," a common epithet for the supreme leader] suggest that until further notice, we are henceforth following the Hassan model.
M. Venizelos' speech was delivered in measured terms, and, while avoiding making any straightforward declaration, he recognized, in fact, that Greece and Crete are henceforth united.
Both Corbyn and Bernie Sanders in the US have been dismissed by some as unelectable, a term Moore says is "shorthand for the phrase 'You are henceforth only permitted to elect conservatives'".
These MD models are henceforth referred to as the bulk MD models.
Edges of this kind are henceforth referred to as copies of both each other and the corresponding measurement.
We admit that there are, henceforth, numerous splendid results on two-weighted norm inequalities but left unmentioned here.
These fifth bands, however, do not penetrate very far below the Fermi level and are henceforth ignored.
The following description utilizes the particular properties of a type of graph whose instances are henceforth called ambiguity graphs.
The relative numbers of hits in the video folder in Bb are henceforth discussed as representing video viewing patterns.
Now, that isn't to say that your UMDs are, henceforth, totally useless, it's just that Sony couldn't figure everything out in time for the system's launch.
