plotimplicit takes three mandatory arguments and
three optional arguments:
expr, an expression of two variables implicitly
defining a curve by expr=0.
vars, a list of the two variables, optionally with
their ranges var=a..b. If a range is not given, the
ranges are determined by WX-, WX+ and WY-, WY+
in the graphical configuration (see Section 3.5.8).
Optionally, xstep, which can be
xstep=n to specify the discretization
step in the x direction.
Optionally, ystep, which can be
ystep=m to specify the discretization
step in the y direction.
Optionally, unfactored.
plotimplicity(expr,vars ⟨xstep,ystep,unfactored⟩)
draws the graphic representation of the curve defined by the implicit equation
expr=0 over the given ranges of the variables.
