diff --git a/src/main.rs b/src/main.rs
index 2ca1032..83a0d5c 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -8,6 +8,7 @@ mod truth_table;
 
 use gray_code::gray_code;
 use truth_table::print_truth_table;
+use negation_normal_form::negation_normal_form;
 
 fn main() {
     println!("Hello, world!");
@@ -22,4 +23,11 @@ fn main() {
     println!("{}", gray_code(3));
     print_truth_table("ZFG|&");
     print_truth_table("ABC|&");
+    let formula = "AB=CD^|!AD!^!&!";
+    println!("{formula}");
+    print_truth_table(formula);
+    let formula = &negation_normal_form(formula);
+    println!("{formula}");
+    print_truth_table(formula);
+
 }
diff --git a/src/negation_normal_form.rs b/src/negation_normal_form.rs
index 2a63e8d..0bbb0fd 100644
--- a/src/negation_normal_form.rs
+++ b/src/negation_normal_form.rs
@@ -2,7 +2,7 @@ mod tests;
 
 use crate::ast::Node;
 
-fn negation_normal_form(formula: &str) -> String {
+pub fn negation_normal_form(formula: &str) -> String {
     let mut ast = Node::<char>::parse_formula(formula);
     ast.simplify();
     Node::<char>::ast_to_formula(&ast)
diff --git a/src/negation_normal_form/tests.rs b/src/negation_normal_form/tests.rs
index 11a1f9c..d99a0a5 100644
--- a/src/negation_normal_form/tests.rs
+++ b/src/negation_normal_form/tests.rs
@@ -63,6 +63,6 @@ mod tests {
 
     #[test]
     fn complex_tests() {
-        assert_eq!("A", "A");
+        assert_eq!(negation_normal_form("AB=CD^|!AD!^!&!"), "A!B|B!A|&CD|C!D!|&|AD!|A!D|&|");
     }
 }