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What is the difference between ? Definition and ?? Information?

If I define two functions for the same symbol

f[x_] := Cos[x]
f[b_, c_] := Sin[b c]

I get the same result for ?f and ??f

enter image description here

I've read the documentation, but it's not giving me a real sense of the difference. Are there different use cases? Can I always use one of these (? or ??) and ignore the other?

ps. Which tags are appropriate for this question?

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  • $\begingroup$ try this $\endgroup$
    – chris
    Apr 9, 2015 at 9:22
  • 1
    $\begingroup$ ?... is the same as Information[..., LongForm -> False] and different from Definition. $\endgroup$
    – Szabolcs
    Apr 9, 2015 at 16:42

1 Answer 1

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Actually, while the input escape ?? is shorthand for Information, ? is not a shorthand for Definition (though ? might use Definition). Basically, if there is a usage message defined, ? returns that, if not, it returns definitions. Information and ?? always return everything accessible. Compare:

In[25]:= f[x_] := Cos[x]
f[b_, c_] := Sin[b c]
f::usage = "blahblah";

Definition@f
 f[x_] := Cos[x]

 f[b_, c_] := Sin[b c]
?f (* prints usage message if exists, Definitions[f] otherwise *)
  blahblah
Information@f (* same as ??f *)
blahblah

f[x_]:=Cos[x]

f[b_,c_]:=Sin[b c]

According to the documentation under Document Constructs:

Mathematica graphics

Of course, any definition is only printed if the symbol is not ReadProtected. Information itself is ReadProtected, hence only attributes and options are listed:

Definition@Information
Attributes[Information] = {HoldAll, Protected, ReadProtected}

Options[Information] = {LongForm -> True}

Compare the above to the extensive output produced by PrintDefinitions, that delves deep into the symbol's definition (large output is omitted):

Needs["GeneralUtilities`"];
PrintDefinitions@Information

Furthermore, you can abuse the ? operator to ask about multiple functions:

?*Chart

Mathematica graphics

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