... ( xj , htxi ) = -xin ( ht , xj ) + ( xi , ht ) xj – Qs ( xi , ht , xj ) , which is obtained by ( 3.13 ) , we have that the difference ( 3.20 ) - ( 3.21 ) is ( 3.23 ) + S xi ( ¥ð ( xjh , t ) –¥ð¥ó xj ) - ¥ð ( ht , xj ) ) + x ; ( ¥ð + ( xi , ht ) ...