Local analysis max yy(u ◆ Welfare s∑1≤n+∑(x)-∑c(q) →∑的(x)-∑c(q)(42 i=1 o So we can metric the welfare by Marshallian aggregate surplus S(xq)=∑(x)-∑cq)Local analysis Welfare So we can metric the welfare by Marshallian aggregate surplus: 1 1 1 1 max ( , ) . . ( ) ( ) I I I J i m i i j j i i j W u u s t u x c q   = = =     + − 1 1 1 ( ) ( ) ( , ) I J i i j j I i j  x c q W u u = =  −    1 1 ( ) ( ) ( ) I J i i j j i j S x c q  = = x,q = −  