plot_contour(cos((x**2 + y**2)) * exp(-(x**2 + y**2) / 10),
     (x, -5, 5), (y, -5, 5))
# Expected:
## Plot object containing:
## [0]: contour: exp(-x**2/10 - y**2/10)*cos(x**2 + y**2) for x over (-5, 5) and y over (-5, 5)