UnderscriptBox[x, y] is the low-level box representation for UnderscriptBox[x, y] in notebook expressions.
Uninstall[link] terminates an external program started by Install, and removes Mathematica definitions set up by it.
ValueQ
(Built-in Mathematica Symbol) ValueQ[expr] gives True if a value has been defined for expr, and gives False otherwise.
$BatchInput is True if input in the current session is being fed directly to the Mathematica kernel in batch mode.
$LicenseID is a string that gives the license ID under which Mathematica is being run.
$MaxPrecision gives the maximum number of digits of precision to be allowed in arbitrary-precision numbers.
$ProcessorCount gives the number of processor cores available on the computer system on which Mathematica is being run.
$RootDirectory gives the root directory of your file system.
$TimedOut is a special symbol returned by certain functions when an operation times out.
When you execute a command like NotebookWrite[obj,data] the actual operation of inserting data into your notebook is performed in the front end. Normally, however, the kernel ...