This question arises out of having Devlin's *Constructibility* [1] in my collection of books at home during the lockdown. Chapter IX of the book deals with Silver machines, which are presented as Silver's attempt at capturing the fine structural content of $L$ using a coherent hierarchy of functions.

Searching for "Silver machine" on MathSciNet yields four results, one of which is Devlin's book and the other three which are currently inaccessible to me on the internet.

Devlin uses Silver machines to prove a global $\square$ principle in $L$, and has an exercise that asks the reader to prove the Covering Lemma(!) using them as well. It appears that this may be done in one of the four references from MathSciNet, and the title of another advertises the construction of a gap-1 morass using Silver's ideas. This shows that such "machines" should have a lot of power, but they also seem to have not attracted the attention of set-theorists.

At an abstract level, I am wondering "Why is this?" and even "What are Silver machines good for?"

For a more concrete question:

Are there significant consequences of V=L for which there is no known "Silver machine proof"? In particular, can one establish the existence of gap-n morasses using Silver machines?

Any references would be appreciated. Devlin's discussion mentions unpublished work of Silver, and also unpublished notes of Litman.

[1] *Devlin, Keith J.*, Constructibility, Perspectives in Mathematical Logic. Berlin etc.: Springer-Verlag. XI, 425 p. DM 158.00; {$} 57.60 (1984). ZBL0542.03029.