diff --git a/lesson_06/expression/src/functions.ts b/lesson_06/expression/src/functions.ts
index ab7433c9c..e193d2f9b 100644
--- a/lesson_06/expression/src/functions.ts
+++ b/lesson_06/expression/src/functions.ts
@@ -1,16 +1,17 @@
-export const FUNCTIONS: Record<string, Function> = Object.freeze({
-  A: (a: number, b: number, c: number, d: number, e: number) =>
-    ((a + b) * c) / Math.pow(d, e),
-  B: (a: number, b: number, c: number, d: number, e: number) =>
-    Math.pow(a + b, c) / (d * e),
-  C: (a: number, b: number, c: number, d: number, e: number) =>
-    a / b + c * Math.pow(d, e),
-  D: (a: number, b: number, c: number, d: number, e: number) =>
-    (a * b) / Math.pow(c + d, e),
-  E: (a: number, b: number, c: number, d: number, e: number) =>
-    Math.pow((a + b) / c, d) * e,
-  F: (a: number, b: number, c: number, d: number, e: number) =>
-    (a * Math.pow(b + c, d)) / e,
-  G: (a: number, b: number, c: number, d: number, e: number) =>
-    ((Math.pow(a, b) + c) * d) / e,
-});
+export const FUNCTIONS: Record<string, (...args: number[]) => number> =
+  Object.freeze({
+    A: (a: number, b: number, c: number, d: number, e: number) =>
+      ((a + b) * c) / Math.pow(d, e),
+    B: (a: number, b: number, c: number, d: number, e: number) =>
+      Math.pow(a + b, c) / (d * e),
+    C: (a: number, b: number, c: number, d: number, e: number) =>
+      a / b + c * Math.pow(d, e),
+    D: (a: number, b: number, c: number, d: number, e: number) =>
+      (a * b) / Math.pow(c + d, e),
+    E: (a: number, b: number, c: number, d: number, e: number) =>
+      Math.pow((a + b) / c, d) * e,
+    F: (a: number, b: number, c: number, d: number, e: number) =>
+      (a * Math.pow(b + c, d)) / e,
+    G: (a: number, b: number, c: number, d: number, e: number) =>
+      ((Math.pow(a, b) + c) * d) / e,
+  });
diff --git a/lesson_06/expression/src/lesson6.test.ts b/lesson_06/expression/src/lesson6.test.ts
index c324ca280..509eb98f5 100644
--- a/lesson_06/expression/src/lesson6.test.ts
+++ b/lesson_06/expression/src/lesson6.test.ts
@@ -17,7 +17,7 @@ describe("Lesson6Test", () => {
     const c = 3;
     const d = 4;
     const e = 5;
-    const expected = FUNCTIONS[process.env.HW_VERSION!].call(
+    const expected = FUNCTIONS[process.env.HW_VERSION || ""].call(
       null,
       ...[a, b, c, d, e],
     );
diff --git a/lesson_06/expression/src/lesson6.ts b/lesson_06/expression/src/lesson6.ts
index bfe71e676..00af72421 100644
--- a/lesson_06/expression/src/lesson6.ts
+++ b/lesson_06/expression/src/lesson6.ts
@@ -13,7 +13,7 @@ const rl = createInterface({
 });
 
 const main = async () => {
-  const testFunction = FUNCTIONS[process.env.HW_VERSION!];
+  const testFunction = FUNCTIONS[process.env.HW_VERSION || ""];
   if (testFunction === undefined) {
     console.log("HW_VERSION version not set in config. Exiting...");
     process.exit(1);
diff --git a/lesson_06/expression/src/utils.ts b/lesson_06/expression/src/utils.ts
index e6f53b6a0..520741a62 100644
--- a/lesson_06/expression/src/utils.ts
+++ b/lesson_06/expression/src/utils.ts
@@ -12,9 +12,9 @@ export const askQuestion = (
   });
 };
 
-export const getFunctionBody = (f: Function) => {
-  const fString = f.toString().split("=>").pop()!;
-  return beautify(fString);
+export const getFunctionBody = (f: () => unknown) => {
+  const fString = f.toString().split("=>").pop();
+  return beautify(fString || "");
 };
 
 export const printFormualaWithValues = (
@@ -34,7 +34,7 @@ export const printFormualaWithValues = (
     ["e", String(e)],
     ["pow", "Math.pow"],
   ).reduce(
-    (acc: string, param: string[]) => acc.replace(param[0]!, param[1]!),
+    (acc: string, param: string[]) => acc.replace(param[0], param[1]),
     functionBody,
   );
   console.log(`\nNow computing the value of ${formula}`);