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Canonical Key
z*cos(z)
Closed Form
f(z) = z*cos(z)

Image domain \(f(\mathbb{D})\)

The image of the unit disk under \(f\): concentric circles \(|z|=r\) and radial spokes mapped through \(f(z)=z+a_2z^2+\dots\); the bold curve is the boundary \(f(e^{i\theta})\). Rendered in your browser from the certified Taylor coefficients - nothing is computed server-side.

Taylor series
r* ≈ 0.800
Radius of starlikeness r* ≈ 0.8000
disproven f is starlike on |z| < r*; the colored disk shows the certified region.

Unit disk explorer - hover to evaluate

Hover over the disk

Related

Univalence Criteria

Schwarzian norm ||S(f)||
1079.510
✗ exceeds Nehari bound 2
Pre-Schwarzian norm ||T(f)||
26.767
✗ exceeds Becker bound 1

Facts (8)

Property Kind Params Holds Value / r Status Confidence
B membership {} 26.7667 ✗ disproven rigorous_verified
K membership {} -1468.7744 unscreened -
N membership {} 1079.5097 ✗ disproven rigorous_verified
||T(f)|| bound {} 26.7667 ✓ proven rigorous_verified
r* radius {} - r ≤ 0.860 🔬 screened numerical_strong
||S(f)|| bound {} 1079.5097 ✓ proven rigorous_verified
S* membership {} r ≤ 0.800 ✗ disproven proven
S membership {} - unscreened -

Verification Runs (6)

Verifier Property Direction Outcome Domain r Witness Engine
boundary_scan_closed_form_v31 starlike disproves pass 0.800 0.9*exp(i*0.024544) boundary_v3.1
pointwise_nehari_univalent_iv nehari_univalent disproves pass 0.864 [0.8636134453781512, 0.0] gft-0.1.0-reaudit-20260610
pointwise_becker_univalent_iv becker_univalent disproves pass 0.864 [0.8636134453781512, 0.0] gft-0.1.0-reaudit-20260610
pointwise_starlike_iv starlike disproves pass 0.990 [0.99, 0.0] gft-0.1.0-reaudit-20260610
boundary_scan_centered_v31 starlike disproves pass 0.800 0.9*exp(i*0.024544) boundary_v3.1
boundary_scan_closed_form starlike disproves pass 0.800 0.9*exp(i*0.024544) boundary_v3.0

Instances (1)

{}
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