Water Contract
<method number.plus _other_unkeyed=opt=<type.vector_of number/>=ekind.code="_body"/>

Plus can add up any number of arguments:

1.<plus 2 3/>

6

1.2.<plus 0.3/>

1.5

<set foo=<vector 2 3 4/> />
0.<plus _args=foo/>

Plus has a default subject of 0

<plus 2 3/>

5