diff --git a/program-analysis/echidna/exercises/exercise1/solution.sol b/program-analysis/echidna/exercises/exercise1/solution.sol
index b48aa29b..cc2ac982 100644
--- a/program-analysis/echidna/exercises/exercise1/solution.sol
+++ b/program-analysis/echidna/exercises/exercise1/solution.sol
@@ -11,8 +11,8 @@ import "./token.sol";
 contract TestToken is Token {
     address echidna = msg.sender;
 
-    constructor() public {
-        balances[echidna] = 10000;
+    constructor() {
+        balances[echidna] = 10_000;
     }
 
     function echidna_test_balance() public view returns (bool) {
diff --git a/program-analysis/echidna/exercises/exercise1/template.sol b/program-analysis/echidna/exercises/exercise1/template.sol
index e20fec9c..33eabf5e 100644
--- a/program-analysis/echidna/exercises/exercise1/template.sol
+++ b/program-analysis/echidna/exercises/exercise1/template.sol
@@ -11,8 +11,8 @@ import "./token.sol";
 contract TestToken is Token {
     address echidna = tx.origin;
 
-    constructor() public {
-        balances[echidna] = 10000;
+    constructor() {
+        balances[echidna] = 10_000;
     }
 
     function echidna_test_balance() public view returns (bool) {
diff --git a/program-analysis/echidna/exercises/exercise2/solution.sol b/program-analysis/echidna/exercises/exercise2/solution.sol
index 6d6f161e..5d49e026 100644
--- a/program-analysis/echidna/exercises/exercise2/solution.sol
+++ b/program-analysis/echidna/exercises/exercise2/solution.sol
@@ -9,7 +9,7 @@ import "./token.sol";
 ///      echidna program-analysis/echidna/exercises/exercise1/solution.sol
 ///      ```
 contract TestToken is Token {
-    constructor() public {
+    constructor() {
         pause(); // pause the contract
         owner = address(0); // lose ownership
     }
diff --git a/program-analysis/echidna/exercises/exercise2/template.sol b/program-analysis/echidna/exercises/exercise2/template.sol
index 69e8b47b..f3ae81da 100644
--- a/program-analysis/echidna/exercises/exercise2/template.sol
+++ b/program-analysis/echidna/exercises/exercise2/template.sol
@@ -9,7 +9,7 @@ import "./token.sol";
 ///      echidna program-analysis/echidna/exercises/exercise2/template.sol
 ///      ```
 contract TestToken is Token {
-    constructor() public {
+    constructor() {
         pause(); // pause the contract
         owner = address(0); // lose ownership
     }
diff --git a/program-analysis/echidna/exercises/exercise3/mintable.sol b/program-analysis/echidna/exercises/exercise3/mintable.sol
index acfa819d..0efc1a98 100644
--- a/program-analysis/echidna/exercises/exercise3/mintable.sol
+++ b/program-analysis/echidna/exercises/exercise3/mintable.sol
@@ -7,7 +7,7 @@ contract MintableToken is Token {
     int256 public totalMinted;
     int256 public totalMintable;
 
-    constructor(int256 totalMintable_) public {
+    constructor(int256 totalMintable_) {
         totalMintable = totalMintable_;
     }
 
diff --git a/program-analysis/echidna/exercises/exercise3/solution.sol b/program-analysis/echidna/exercises/exercise3/solution.sol
index 0d6dd92e..ec2da92d 100644
--- a/program-analysis/echidna/exercises/exercise3/solution.sol
+++ b/program-analysis/echidna/exercises/exercise3/solution.sol
@@ -11,11 +11,11 @@ import "./mintable.sol";
 contract TestToken is MintableToken {
     address echidna = msg.sender;
 
-    constructor() public MintableToken(10000) {
+    constructor() MintableToken(10_000) {
         owner = echidna;
     }
 
     function echidna_test_balance() public view returns (bool) {
-        return balances[msg.sender] <= 10000;
+        return balances[msg.sender] <= 10_000;
     }
 }
diff --git a/program-analysis/echidna/exercises/exercise3/template.sol b/program-analysis/echidna/exercises/exercise3/template.sol
index 63f8ffdc..9a9c01d7 100644
--- a/program-analysis/echidna/exercises/exercise3/template.sol
+++ b/program-analysis/echidna/exercises/exercise3/template.sol
@@ -12,7 +12,7 @@ contract TestToken is MintableToken {
     address echidna = msg.sender;
 
     // TODO: update the constructor
-    constructor(int256 totalMintable) public MintableToken(totalMintable) {}
+    constructor(int256 totalMintable) MintableToken(totalMintable) {}
 
     function echidna_test_balance() public view returns (bool) {
         // TODO: add the property