     case Exists(String)
     case DoesNotExist(String)
     case HasPrefix(key: String, prefix: String)
-}
+    case LessThan(key: String, value: Double)
+    case Limit(Int)
+  }
 
 extension Constraint :Equatable {}
 

    case .HasPrefix(key: let lKey, prefix: let lPrefix):
        switch (rhs) {
        case .HasPrefix(key: let rKey, prefix: let rPrefix) where lKey == rKey && lPrefix == rPrefix:
            return true
        default:
            return false

            case .HasPrefix(key: let key, prefix: let prefix):
                q.whereKey(key, hasPrefix: prefix)
                break
            case .Limit(let limit):
                q.limit = limit
            }
        }

