fix intersection for degenerate intervals

Author: victorpoughon

src/compare.ts

@@ -1,5 +1,5 @@
 import { Interval } from "./interval.ts";
-import { Union, typeCheckIsIntervalOrUnion, toUnion, EMPTY } from "./union.ts";
+import { Union, typeCheckIsIntervalOrUnion, toUnion, EMPTY, union } from "./union.ts";
 
 export function ioverlap(a: Interval, b: Interval): boolean {
     return a.hi >= b.lo && a.lo <= b.hi;
@@ -96,7 +96,8 @@ export function ucomplement(U: Union): Union {
         result.push(new Interval(U.intervals[U.intervals.length - 1].hi, Infinity));
     }
 
-    return new Union(result);
+    // Need to call the union constructor, because some intervals might touch
+    return union(result);
 }
 
 // Complement of a union or interval

tests/compare.test.ts

@@ -187,6 +187,14 @@ describe("intersection of unions", () => {
 
 describe("complement of a union", () => {
     it("real union", () => {
+        assert.deepEqual(
+            nsf.complement(nsf.union([int(3, 8)])),
+            nsf.union([int(-inf, 3), int(8, inf)])
+        );
+
+        assert.deepEqual(nsf.complement(nsf.union([int(0, 0)])), nsf.union([nsf.FULL]));
+        assert.deepEqual(nsf.complement(nsf.union([int(0, 0), int(1, 1)])), nsf.union([nsf.FULL]));
+
         assert.deepEqual(
             nsf.complement(nsf.union([int(3, 8), int(12, 13), int(15, 16), int(17, 18)])),
             nsf.union([int(-inf, 3), int(8, 12), int(13, 15), int(16, 17), int(18, inf)])