def Map.keys.go
import Base3024def Map.keys.go(a, -V: Kind(a), m: Map<a, V>, acc: List<&2, String>) ->
3025 List<&2, String>:
3026 match m:
3027 case MTip{}:
3028 acc
3029 case MLeaf{k, v}:
3030 k <> acc
3031 case MNode{pos, lo, hi}:
3032 Map.keys.go(a, V, lo, Map.keys.go(a, V, hi, acc))