kills global variables
clearglobal()
clearglobal nam1 ... namn
clearglobal('nam1', ...,'namn')
:nam1,..., namn valid variable names :
clearglobal() kills all the global variables.
clearglobal nam1 ... namn kills the global variables given by their names.
Note that clearglobal() only clears the global variables, the local copies of these global variables are not destroyed.
`global`_ a b c
a=1;b=2;c=3;
who('global')
clearglobal b
who('global')