Strong gravitational lensing's 'external shear' is not shear - Etherington, Amy; Nightingale, James W; Nightingale, James W; Massey, Richard; Tam, Sut-Ieng; Cao, Xiaoyue; Niemiec, Anna; He, Qiuhan; Robertson, Andrew; Li, Ran; Amvrosiadis, Aristeidis; Cole, Shaun; et al. (Monthly Notices Of The Royal Astronomical Society, 2024)