Alternate method

Choosing a window with the `WINDOW` command, which has its lower left corner at `(lowx,lowy)` and its upper right corner at `(upx,upy)`, is equivalent to choosing the graphics sub-window with the `SET` command. That is, the following command:

`WINDOW n lowx lowy upx upy`

is equivalent to the following:

     SET %XLOWERWINDOW lowx
     SET %YLOWERWINDOW lowy
     SET %XUPPERWINDOW upx
     SET %YUPPERWINDOW upy

Using the `SET` command to define a window is not recommended. When the `CLEAR` command is entered, the window chosen with the last `WINDOW` command is set up, and the values of `XLOWERWINDOW`, `XUPPERWINDOW`, `YLOWERWINDOW`, and `YUPPERWINDOW` are changed. Thus, if their values had been re-defined with the `SET> command, these values would be lost when the `CLEAR` command is entered.`

Pre-defined windows
Multiple window creation