Nothing
plotFun(f(x, y) ~ x + y, x.lim = c(-3.5, 3.5), y.lim = c(-2, 2), npts = 150)
plotFun(g(x, y) ~ x + y, x.lim = c(-3.5, 3.5), y.lim = c(-2, 2), npts = 150)
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