     GRPN is a graphical reverse polish notation (RPN) calculator.

     GRPN works with  real  numbers,  complex  numbers,  matrices,  and  complex
     matrices.  Numbers can be displayed in 4 different radix modes, and complex
     numbers can be displayed in either Cartesian or polar form.

     GRPN uses a stack and reverse polish notation to evaluate expressions.  The
     stack in GRPN is infinite and limited only by available memory.

     Expressions are evaluated in reverse polish notation.  Unlike  conventional
     (prefix) notation, RPN requires that all arguments to a command are entered
     prior to execution of the command.

     For example to add 6.7 to 3.2 you would push both numbers onto  the  stack,
     then press the add (+) button:

     3.2<enter> 6.7<enter> +

     The result is left on the stack.

     Note that GRPN uses a shorthand for all commands that causes  an  automatic
     <enter>  before  executing  a  command.  The previous example could then be
     done as:

     3.2<enter>
     6.7+

     Input is accepted from both the keyboard and the mouse.   When  entering  a
     command  from  the keyboard, the command may be abbreviated to the shortest
     set of letters which uniquely identifies the command.  Mouse  input  simply
     requires pressing the button with the desired command.

     Available commands:

     +               Add.
     -               Subtract.
     *               Multiply.
     /               Divide.
     ^               Power.
     <enter>         Push a number onto the top of the stack.
     <space>         Push a number onto the top of the stack.
     dup             Copy the number on the top of the stack.
     neg             Change sign.
     drop            Delete the number on the top of the stack.
     swap            Swap 2 numbers on the top of the stack.
     pi              The constant PI.
     sin             Trigonometric function Sin.
     cos             Trigonometric function Cos
     tan             Trigonometric function Tan.
     inv             Inverse.
     asin            Trigonometric function Arc-sin
     acos            Trigonometric function Arc-cos.
     atan            Trigonometric function Arc-tan.
     sqrt            Square root.
     nroot           N-th root.
     log             Log base 10
     ln              Natural log (log base e).
     sqr             Square.