Isochronous islands in the two-harmonic standard mapMichele Mugnaine, Bruno B. Leal, Alfredo M. Ozorio de Almeida, Ricardo L. Viana and Iberê L. CaldasEur. Phys. J. Spec. Top., 234 25 (2026) 7851-7858DOI: https://doi.org/10.1140/epjs/s11734-025-01867-7