D O C U M E N T 5 2 3 M AY 1 9 2 9 7 3 9 ALf. [18 340]. [1] Dated by the observation that Einstein is using a notation for the tetrads with both indices to the right-hand side and leg-index to the left of the coordinate index, which he began using in Doc. 521. [2] The following calculations were written on the back of the page. [3] The following four lines were written with pencil. [4] The operator was introduced in Doc. 459, eq. (5). h s h s h s – h t = h t h t h t – = h s h s h s – = h s h s h s h s h s – h s h s h s – D G 2 0 D ( H 2 (H ) / ) – 0 h s h s h s h s – i lm ilm - i lm - i lm 1 2 -- S i i – lm ilm S lm m l l m – – ilm | 1 2 --S i lm + 1 2 -- i m l l m S lm – + + S 1 2 S / = 1 2 --S i lm i S lm i m l ) + – S / = S + S / / [2] [4] [[3] ] D