diff --git a/src/index.ts b/src/index.ts
index a7f8a2e1ec441ea65b4b100f6e4890a02794d862..059f59cb3bc43bec06e548a7f378e07bb373398d 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -17,6 +17,7 @@ export * from './util/numericalstring';
 export * from './util/message';
 export * from './util/log';
 export * from './util/result';
+export * from './util/pair';
 export * from './util/interval';
 export * from './pab/pab_dimension';
 export * from './pab/pab_puissance';
diff --git a/src/util/interval.ts b/src/util/interval.ts
index 753c791a1dbdb23990be3c7bad07bc6e918b084b..756dc2cbe5c11b813873f565ae6ba5bc39a6e2ec 100644
--- a/src/util/interval.ts
+++ b/src/util/interval.ts
@@ -37,8 +37,4 @@ export class Interval extends Pair {
     setBounds(i: Pair) {
         this.setPair(i);
     }
-
-    toString(): string {
-        return "[" + this.min + "," + this.max + "]";
-    }
 }
diff --git a/src/util/pair.ts b/src/util/pair.ts
index 9a421b4c7e8e15617f55c4727ab5cfc16ccfee89..ab9c56b168bf9a102bf7bd622308b7de6c584e3c 100644
--- a/src/util/pair.ts
+++ b/src/util/pair.ts
@@ -42,4 +42,8 @@ export class Pair {
     intervalHasValue(v: number) {
         return this.min <= v && v <= this.max;
     }
+
+    toString(): string {
+        return "[" + this.min + "," + this.max + "]";
+    }
 }