Question: how do i get rid out of error for ploting hardening and softening spring code?

restart; with(plots, implicitplot);
print(`output redirected...`); # input placeholder
                         [implicitplot]
p; .2; omega[0] := 1; epsilon[1] := 1.04493; epsilon[2] := .93259; delta := 0.2e-1;
eq := [[omega[0]*a-a*Omega^2+(3/4)*epsilon[2]*a^3]^2+(delta*Omega*a)^2 = p^2];
print(`output redirected...`); # input placeholder
implicitplot(eq, omega = .5 .. 2, a = 0 .. 5, p = 0 .. 1, color = blue, thickness = 2, gridrefin = 6);
%;
Error, (in plots/implicitplot) invalid input: the following extra unknowns were found in the input expression: {Omega, p}

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