Make Set concat partial
@@ -528,7 +528,7 @@ number of unbound keys being mached. In other words, one unbound variable is
linear, two is quadratic, three is cubic, etc.
```k
- syntax Set ::= Set Set [left, function, total, hook(SET.concat), klabel(_Set_), symbol, assoc, comm, unit(.Set), idem, element(SetItem), format(%1%n%2)]
+ syntax Set ::= Set Set [left, function, hook(SET.concat), klabel(_Set_), symbol, assoc, comm, unit(.Set), idem, element(SetItem), format(%1%n%2)]
```
### Set unit
