The standard siren approach of gravitational wave cosmology appeals to thedirect luminosity distance estimation through the waveform signals frominspiralling double compact binaries, especially those with electromagneticcounterparts providing redshifts. It is limited by the calibrationuncertainties in strain amplitude and relies on the fine details of thewaveform. The Einstein Telescope is expected to produce $10^4-10^5$gravitational wave detections per year, $50-100$ of which will be lensed. Herewe report a waveform-independent strategy to achieve precise cosmography bycombining the accurately measured time delays from strongly lensedgravitational wave signals with the images and redshifts observed in theelectromagnetic domain. We demonstrate that just 10 such systems can provide aHubble constant uncertainty of $0.68\%$ for a flat Lambda Cold Dark Matteruniverse in the era of third generation ground-based detectors.
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