Index: node_modules/d3-array/src/union.js
===================================================================
--- node_modules/d3-array/src/union.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
+++ node_modules/d3-array/src/union.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
@@ -0,0 +1,11 @@
+import {InternSet} from "internmap";
+
+export default function union(...others) {
+  const set = new InternSet();
+  for (const other of others) {
+    for (const o of other) {
+      set.add(o);
+    }
+  }
+  return set;
+}