def usage(self, use_pager=True):
        """
        Returns the basic description of using the Tachyon raytracer (simply what is returned by running tachyon with no input).  The output is paged unless use_pager=False.

        TESTS::

            sage: from sage.interfaces.tachyon import TachyonRT
            sage: t = TachyonRT()
            sage: t.usage(use_pager=False)
            Tachyon Parallel/Multiprocessor Ray Tracer   Version...
        """
        r = os.popen('tachyon').read()
        if use_pager == True:
            pager()(r)
        else:
            print r

    def help(self, string):
        """
        Display Giac help about string.

        This is the same as typing "?string" in the Giac console.

        INPUT:

        -  ``string`` -- a string to search for in the giac help system

        EXAMPLES::

            sage: giac.help('Psi')         # not tested - depends of giac and $LANG
            Psi(a,n)=nth-derivative of the function DiGamma ([email protected]) at point a (Psi(a,0)=Psi(a))...
        """
        pager()(self._help(string))

    def help(self, str):
        """
        Display Maple help about str. This is the same as typing "?str" in
        the Maple console.

        INPUT:

        -  ``str`` - a string to search for in the maple help
           system

        EXAMPLES::

            sage: maple.help('digamma') #not tested
            Psi - the Digamma and Polygamma functions
            ...
        """
        pager()(self._help(str))

    def source(self, s):
        """
        Display the Maple source (if possible) about s. This is the same as
        returning the output produced by the following Maple commands:

        interface(verboseproc=2): print(s)

        INPUT:

        -  ``s`` - a string representing the function whose
           source code you want

        EXAMPLES::

            sage: maple.source('curry')  #not tested
            p -> subs('_X' = args[2 .. nargs], () -> p(_X, args))
        """
        try:
            pager()(self._source(s))
        except Exception:
            pager()('No source code could be found.')

 def usage(self):
     r = os.popen('povray').read()
     pager()(r)

    def help(self, use_pager=True):
        """
        Prints (pages) the help file written by John Stone describing scene files for Tachyon.  The output is paged unless use_pager=False. 

        TESTS::

            sage: from sage.interfaces.tachyon import TachyonRT
            sage: t = TachyonRT()
            sage: t.help(use_pager=False)
            This help, which was written by John Stone, describes ...
        """
        s = r"""
This help, which was written by John Stone, describes how to create
scene files.
        
At the present time, scene description files are very simple.  
The parser can't handle multiple file scene descriptions, although they
may be added in the future.  Most of the objects and their scene description
are closely related to the RAY API 
\emph{(See the API docs for additional info.)}

\subsection{Basic Scene Requirements}
  Unlike some other ray tracers out there, RAY requires that you 
specify most of the scene parameters in the scene description file itself.
If users would rather specify some of these parameters at the command line,
then I may add that feature in the future.  
A scene description file contains keywords, and values associated or grouped
with a keyword.  All keywords can be in caps, lower case, or mixed case
for the convenience of the user.  File names and texture names are 
normally case-sensitive, although the behavior for file names is 
operating system-dependent.  All values are either character strings, or
floating point numbers.  In some cases, the presence of one keyword will
require additional keyword / value pairs. 

  At the moment there are several keywords with values, 
that must appear in every scene description file.  
Every scene description file must begin with the 
{\bf BEGIN\_SCENE} keyword, and end with the {\bf END\_SCENE} keyword.
All definitions and declarations of any kind must be inside the 
{\bf BEGIN\_SCENE}, {\bf END\_SCENE} pair.
The {\bf RESOLUTION} keyword is followed by an x resolution
and a y resolution in terms of pixels on each axis.  There are currently 
no limits placed on the resolution of an output image other than the
computer's available memory and reasonable execution time.
An example of a simple scene description skeleton is show below:
\begin{verbatim}
BEGIN_SCENE
  RESOLUTION 1024 1024 
...
...  Camera definition..
...
...  Other objects, etc..
...

END_SCENE
\end{verbatim}

\subsection{Camera and viewing parameters}
  One of the most important parts of any scene, is the camera position and
orientation.  Having a good angle on a scene can make the difference between
an average looking scene and a strikingly interesting one.  There may be
multiple camera definitions in a scene file, but the last camera definition
overrides all previous definitions.
There are several parameters that control the camera in \RAY, 
{\bf PROJECTION}, {\bf ZOOM}, {\bf ASPECTRATIO}, {\bf ANTIALIASING},
 {\bf CENTER}, {\bf RAYDEPTH}, {\bf VIEWDIR}, and {\bf UPDIR}.  

The first and last keywords required in the definition of a camera are the 
{\bf CAMERA} and {\bf END\_CAMERA} keywords.  The {\bf PROJECTION} keyword 
is optional, the remaining camera keywords are required, and must be 
written in the sequence they are listed in the examples in this section.

\subsubsection{Camera projection modes}
  The {\bf PROJECTION} keyword must be followed by one of the supported
camera projection mode identifiers {\bf PERSPECTIVE}, {\bf PERSPECTIVE_DOF}, 
{\bf ORTHOGRAPHIC}, or {\bf FISHEYE}.  The {\bf FISHEYE} projection mode 
requires two extra parameters {\bf FOCALLENGTH} and {\bf APERTURE} 
which precede the regular camera options.

\begin{verbatim}
Camera
  projection perspective_dof
  focallength 0.75
  aperture 0.02
  Zoom 0.666667
  Aspectratio 1.000000
  Antialiasing 128
  Raydepth 30
  Center  0.000000 0.000000 -2.000000
  Viewdir -0.000000 -0.000000 2.000000
  Updir   0.000000 1.000000 -0.000000
End_Camera
\end{verbatim}

\subsubsection{Common camera parameters}
  The {\bf ZOOM} parameter controls the camera in a way similar to a 
telephoto lens on a 35mm camera.  A zoom value of 1.0 is standard, 
with a 90 degree field of view.  By changing the zoom factor to 2.0, 
the relative size of any feature in the frame is twice as big, while 
the field of view is decreased slightly.  The zoom effect is 
#.........这里部分代码省略.........

    def help(self, topic, pager=True):
        r"""
        Print help on the given topic.

        INPUT:

        - ``topic`` -- string

        EXAMPLES::

            sage: gap3.help('help', pager=False)           #optional - gap3
            Help _______________________________________________________...
            <BLANKLINE>
            This  section describes  together with  the following sectio...
            help system.  The help system lets you read the manual inter...

        ::

            sage: gap3.help('SymmetricGroup', pager=False) #optional - gap3
            no section with this name was found

        TESTS::

            sage: m = gap3([[1,2,3],[4,5,6]]); m           #optional - gap3
            [ [ 1, 2, 3 ], [ 4, 5, 6 ] ]
            sage: gap3.help('help', pager=False)           #optional - gap3
            Help _______________________________________________________...
            sage: m                                        #optional - gap3
            [ [ 1, 2, 3 ], [ 4, 5, 6 ] ]
            sage: m.Print()                                #optional - gap3
            [ [ 1, 2, 3 ], [ 4, 5, 6 ] ]
            sage: gap3.help('Group', pager=False)          #optional - gap3
            Group ______________________________________________________...
            sage: m                                        #optional - gap3
            [ [ 1, 2, 3 ], [ 4, 5, 6 ] ]
            sage: m.Print()                                #optional - gap3
            [ [ 1, 2, 3 ], [ 4, 5, 6 ] ]
        """

        import pexpect
        if self._expect is None:
            self._start()
        E = self._expect
        helptext = []

        # we request the help document
        E.sendline("? %s" % topic)
        # it seems necessary to skip TWO echoes (as is done in the GAP4 interface)
        E.expect("\r\n")
        E.expect("\r\n")

        # next we process the help document; translating special characters, etc.
        while True:
            try:
                x = E.expect_list(self._compiled_full_pattern, timeout=2)
            except pexpect.TIMEOUT:
                break
            if x == 1:
                # matched @@; replace with @
                helptext.append('@')
                helptext.append(E.before)
            elif x == 2:
                # matched a special char; convert and insert
                helptext.append(chr(ord(E.after[1:2])-ord('A')+1))
                helptext.append(E.before)
            elif x == 10:
                # matched @n (normal input mode); it seems we're done
                break
            elif x==11:
                # matched @r (echoing input); skip to end of line
                E.expect_list(self._compiled_small_pattern)

        # merge the help text into one string and print it.
        helptext = "".join(helptext).strip()
        if pager is True:
            import sage.misc.pager
            pager.pager()(helptext)
        else:
            print helptext