diff --git a/include/NR.h b/include/NR.h
index 2c67fa0..5799569 100644
--- a/include/NR.h
+++ b/include/NR.h
@@ -33,7 +33,9 @@ class NR {
 	NR& operator*=(const NR& opNR);
 	NR& operator/=(const NR& opNR);
 
-	void Invert();
+	NR operator-() const;
+
+	NR Inverse() const;
 
 	friend std::ostream& operator<<(std::ostream& os, const NR& opNR);
 	friend std::istream& operator>>(std::istream& os, NR& opNR);
diff --git a/src/NR.cpp b/src/NR.cpp
index b32d64e..19526b2 100644
--- a/src/NR.cpp
+++ b/src/NR.cpp
@@ -19,6 +19,7 @@ NR::NR(int entier) : m_Numerator(entier), m_Denominator(1) {}
 NR::NR(int numerator, int denominator) :
 	m_Numerator((denominator > 0) ? numerator : -numerator), m_Denominator(std::abs(denominator)) {
 	assert(denominator != 0);
+	Reduce();
 }
 
 void NR::Reduce() {
@@ -27,8 +28,9 @@ void NR::Reduce() {
 	m_Numerator /= divisor;
 }
 
-void NR::Invert() {
-	*this = NR(m_Denominator, m_Numerator);
+NR NR::Inverse() const {
+	assert(*this != 0);
+	return {m_Denominator, m_Numerator};
 }
 
 int NR::GetNumerator() const {
@@ -128,3 +130,7 @@ NR& NR::operator/=(const NR& opNR) {
 	*this = *this / opNR;
 	return *this;
 }
+
+NR NR::operator-() const {
+	return {-m_Numerator, m_Denominator};
+}
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