Distance redshift relation in Swiss cheese universe has been investigated by Ronald Kantowski in 1969,[5] and Dyer & Roeder in the 1970s.[6] The gravitational lensing theory for a single embedded point mass lens in flat pressure-less Friedman-Lemaître-Robertson-Walker (FLRW) background universe with non-zero cosmological constant has been built by Ronald Kantowski, Bin Chen, and Xinyu Dai in a series papers.[7][8][9][10]