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Equilibria correspond to the roots of the right-hand side function $f(z) = 4z - z^3 + C$. As C increases, the graph of $f(z)$ shifts vertically upward.

Conditions: The differential equation is $dz/dt = 4z - z^3 + C$.; $C = 4$, which is greater than the critical value C* ≈ 3.079.

Equilibria correspond to the roots of the right-hand side function $f(z) = 4z - z^3 + C$. As C increases, the graph of $f(z)$ shifts vertically upward.

Conditions: The differential equation is $dz/dt = 4z - z^3 + C$.; $C = 4$, which is greater than the critical value C* ≈ 3.079.