a factor of 30, although multiple images were not resolved. The first fully resolved image configuration of a lensed supernova was reported by @Kel2015. The supernova (SN Refsdal) was a core-collapse type [@Kel2016] and lensed by an intervening galaxy cluster and a massive galaxy in the cluster. The second example of a fully resolved lensed supernova was iPTF16geu [@Goo2017]. Detected as an exceptionally luminous supernova (for its redshift) in a regular transient survey, the intermediate Palomar Transient Factory (iPTF), it was subsequently observed by ESO VLT, Keck Observatory, and the Hubble Space Telescope whose images revealed a quadrupole lensing configuration with a sub-arcsec scale of image separations. The supernova was classified as a type Ia SN [@Goo2017; @Can2018]. High-cadence imaging of massive galaxy clusters with HST also recently resulted in the discovery of a new type of lensed transients which appeared to be strongly lensed individual stars [@Rod2018; @Kel2018; @Chen2019; @Kau2019].

Strongly lensed supernovae are unique objects in several respects, making them a promising tool for constraining cosmological parameters such as the Hubble constant [@Gri2018; @Vega2018]. With well-studied light curves, reasonably well-represented by simple models, lensed supernovae appear to be suitable for precise measurements of time delays from even relatively 