plotimplicit takes four mandatory arguments and
three optional arguments:
expr, an expression of three variables implicitly
defining a curve by expr=0.
xvar, yvar and zvar, the first,
second and third variables,optionally with
their ranges var=a..b.
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, zstep, which can be
zstep=p to specify the discretization
step in the y direction.
Optionally, unfactored.
plotimplicity(expr,xvar,yvar,zvar ⟨xstep,ystep,zstepunfactored⟩)
draws the graphic representation of the surface defined by the implicit equation
expr=0 over the given ranges of the variables.