Perhaps he is only human like me. I demand an analysis, whatever damn coordinate system he likes, which is the Kerr-Schild. I am not impressed, rather I am impressed by good field analysis. Sure it is sweet to have an unchanging DETERMINANT. No big deal: this is a locally altered (as per the twisting and such) x,y,z coord system. IT CONTAINS KERR’S ‘r’ also. YOU CAN’T GET AWAY FROM IT.