Functions
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  Some Dust-commands (e.g. FUNC) require mathematical expressions.

   1.Parameters you can ommit:
     X0 - initial x-coordinate
     Y0 - initial y-coordinate
     Z0 - initial z-coordinate
     T0 - parameter
   Example: You want to plot the 2D-Function sin(x^2+y^2):
    -load a plane (dimensions -50..-50,-50..50,0..0)
    -now enter "func(2,"30*sin(x0*x0/30+y0*y0/30)",0,z)"
   This uses the x- and y-coordinates to modify the"
   z-coordinate of the plane."

   2.Constants
     'pi', 'ee' (2.71..)

   3.Operators
     '+','-', ':-(', '/', '^'

   4.Functions
     'sin', 'cos', 'tan', 'cot' , 'asn', 'acs', 'atn', 'act'
     'sinh', 'cosh', 'tanh', 'coth', 'asnh', 'acsh', 'atnh', 'acth'
     'ln', 'log', 'exp', 'sqrt','abs', 'sign', 'int', 'rnd'

  NOTES: 1.Don't forget to enclose your expressions by quotes.
         2.All angles in degrees.