| At | u@:v _ _ _ | 
| @: is equivalent to @ except that  ranks are infinite. | 
   x=: 1 2 3 4
   y=: 7 5 3 2
   x */ @: + y                 Applies product over sums to the entire lists
2016
       
   x */ @ + y                  Applies product over sums to each item of the list
8 7 6 6
     
   + b. 0
0 0 0
   */ @: + b. 0
_ _ _
   */ @ + b. 0
0 0 0