That's a nice shorthand. AIUI, Arc uses [... _ ....] as a terse shorthand for closures, but can only deal with functions that take one argument that way -- thou

That's a nice shorthand. AIUI, Arc uses [... _ ....] as a terse shorthand for closures, but can only deal with functions that take one argument that way -- though it would be simple to expand Arc so it could say [+ _ _2]. Now I've thought about it, I may add something similar as syntax in Unify: (tn + _ _2) (where tn stands for "terse function")