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max( f(abs(x), abs(y)), f(abs(y), abs(x)) ) > 0

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(1) f(x,y) = ax^2 - y + b (parabola)

a = 0.035, b = 0.85

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(2) f(x,y) = x^2 + (y - a)^2 - b^2 (circle)

a = 15.6, b = 14.75

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(3) f(x,y) = abs(x)^p + abs(y - a)^p - b^p (superellipse)

a = 15.6, b = 14.75

p = 2.5, 2.4, 2.3, ...,1.5

p = 4, a = 10, b = 8

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(4) f(x,y) = a[exp(-abs(x+b)^p) + exp(-abs(x-b)^p)] - y + c

p = 1.5, a = 1, b = 7, c = 2

p = 3, a = 1, b = 7, c = 2

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(5) f(x,y) = a cos(bx)^p - y + c

p = 1, a = -1, b = π/7, c = 2

p = 2, a = 1, b = π/7, c = 2

p = 3, a = -1, b = π/7, c = 2

p = 4, a = 1, b = π/7, c = 2

( Mathematical software used: Graph )