diff --git a/server/spec/utils/spans.jest.ts b/server/spec/utils/spans.jest.ts
index 40900bf..8bf3104 100644
--- a/server/spec/utils/spans.jest.ts
+++ b/server/spec/utils/spans.jest.ts
@@ -7,7 +7,7 @@ function cutSpan(from: number, to: number, cuts: [number, number][]): [number, n
   return cutSpanWithSpans(
     { from: from, to: to },
     cuts.map(([from, to]) => ({ from, to }))
-  ).map(({ from, to }) => [from, to]);
+  ).map(({ from, to }) => [from, to] as [number, number]);
 }
 
 describe('cutSpanWithSpans', function() {
diff --git a/server/src/utils/spans.ts b/server/src/utils/spans.ts
index d3a6eeb..7c58450 100644
--- a/server/src/utils/spans.ts
+++ b/server/src/utils/spans.ts
@@ -23,7 +23,7 @@ export function cutSpanWithSpans(inputSpan: Span, cutSpans: Span[]): Span[] {
 
   // we sort and merge out cuts to normalize it
   cutSpans = _.sortBy(cutSpans, s => s.from);
-  var mergedSortedCuts =_.reduce(cutSpans, 
+  const mergedSortedCuts =_.reduce(cutSpans, 
     ((acc: Span[], s: Span) => {
       if(acc.length === 0) return [s];
       let last = acc[acc.length - 1];
@@ -38,20 +38,20 @@ export function cutSpanWithSpans(inputSpan: Span, cutSpans: Span[]): Span[] {
   );
 
   // this is what we get if we cut `mergedSortedCuts` from (-Infinity, Infinity)
-  var holes = mergedSortedCuts.map((cut, i) => {
+  const holes = mergedSortedCuts.map((cut, i) => {
     let from = -Infinity;
     let to = cutSpans[0].from;
     if(i > 0) {
       from = mergedSortedCuts[i - 1].to;
       to = cut.from;
     }
-    return { from, to }
+    return { from, to };
   }).concat({
     from: mergedSortedCuts[mergedSortedCuts.length - 1].to,
     to: Infinity
   });
 
-  return _(holes).map(c => {
+  const holesInsideInputSpan = _(holes).map(c => {
     if(c.to <= inputSpan.from) return undefined;
     if(inputSpan.to <= c.from) return undefined;
     return {
@@ -60,4 +60,5 @@ export function cutSpanWithSpans(inputSpan: Span, cutSpans: Span[]): Span[] {
     }
   }).compact().value();
 
+  return Array.from(holesInsideInputSpan);
 }