Let R {\displaystyle {}R} be a ring, and let a , b , c , a 1 , … , a r , b 1 , … , b s {\displaystyle {}a,b,c,a_{1},\ldots ,a_{r},b_{1},\ldots ,b_{s}} denote elements from R {\displaystyle {}R} . Then the following statements hold.
(rules for sign).