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Getting Information about Mathematica Objects

You can ask for information about any object, whether it is built into Mathematica, has been read in from a Mathematica package, or has been introduced by you.
?Nameshow information on Name
??Nameshow extra information on Name
?Aaaa*show information on all objects whose names begin with Aaaa

Ways to get information directly from the Mathematica kernel.

When you are using Mathematica through the notebook-based interface, ?name gives you usage information with a link to the documentation for the function.
This gives information on the built-in function Log.
When you use ? to get information, you must make sure that the question mark appears as the first character in your input line. You need to do this so that Mathematica can tell when you are requesting information rather than giving ordinary input for evaluation.
You can get extra information by using ??. Attributes is discussed in "Attributes".
This gives information on all Mathematica objects whose names begin with Log. When there is more than one object, Mathematica just lists their names.
?Aaaa will give you information on the particular object whose name you specify. Using the "metacharacter" *, however, you can get information on collections of objects with similar names. The rule is that * is a "wild card" that can stand for any sequence of ordinary characters. So, for example, ?Lo* gets information on all objects whose names consist of the letters Lo, followed by any sequence of characters.
You can put * anywhere in the string you ask ? about. For example, ?*Expand would give you all objects whose names end with Expand. Similarly, ?x*0 would give you objects whose names start with x, end with 0, and have any sequence of characters in between. (You may notice that the way you use * to specify names in Mathematica is similar to the way you use * in Unix and other operating systems to specify file names.)
You can ask for information on most of the special input forms that Mathematica uses. This asks for information about the := operator.