# Why only up to two \[Prime] superscripts are interpreted as derivatives?

I noticed that only up to two \[Prime] superscripts are interpreted as derivatives. Is there a reason for this restriction? Is it documented?

\!$$\*SuperscriptBox["Sin","\[Prime]"][x]$$
(* Cos[x] *)

\!$$\*SuperscriptBox["Sin","\[Prime]\[Prime]"][x]$$
(* -Sin[x] *)

\!$$\*SuperscriptBox["Sin","\[Prime]\[Prime]\[Prime]"][x]$$
(* (Sin^\[Prime]\[Prime]\[Prime])[x] *)


The regular apostrophe can be used any number of times though:

Sin'''[x]
(* -Cos[x] *)

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It is sort-of Documented in that only Prime and DoublePrime are defined.. –  george2079 Oct 21 '13 at 18:00

I believe it is not a restriction, but this comes with the way how Mathematica formats derivatives. That being said, the same way you cannot use 3 superscript primes to input a third derivative, you won't see 3 primes in the output either.

D[f[x], x, x, x]


gives

If you could type this as input, then you would have a way to specify your third derivative with a superscript. Unfortunately, there is a hidden TagBox in the above superscript which cannot be entered easily.

To answer your question: You can use superboxed primes as input for derivative, because Mathematica interprets your box expression correctly. Since 3 primes never occur to represent the third derivative, you cannot use it as valid input.

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