diff --git a/lib/pddl/include/pddl/AST.h b/lib/pddl/include/pddl/AST.h
index 704c17c..1804e18 100644
--- a/lib/pddl/include/pddl/AST.h
+++ b/lib/pddl/include/pddl/AST.h
@@ -292,6 +292,19 @@ struct Either: public NAry<Either<Argument>, Argument>
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
+template<class ArgumentLeft, class ArgumentRight>
+struct Equals: public Binary<Equals<ArgumentLeft, ArgumentRight>, ArgumentLeft, ArgumentRight>
+{
+	static constexpr const auto Identifier = "=";
+
+	explicit Equals(ArgumentLeft &&argumentLeft, ArgumentRight &&argumentRight)
+	:	Binary<Equals<ArgumentLeft, ArgumentRight>, ArgumentLeft, ArgumentRight>(std::move(argumentLeft), std::move(argumentRight))
+	{
+	}
+};
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
 template<class Argument>
 struct Exists: public Quantified<Exists<Argument>, Argument>
 {
diff --git a/lib/pddl/include/pddl/ASTForward.h b/lib/pddl/include/pddl/ASTForward.h
index 8ea4e16..69203bc 100644
--- a/lib/pddl/include/pddl/ASTForward.h
+++ b/lib/pddl/include/pddl/ASTForward.h
@@ -70,6 +70,10 @@ template<class Argument>
 struct Either;
 template<class Argument>
 using EitherPointer = std::unique_ptr<Either<Argument>>;
+template<class ArgumentLeft, class ArgumentRight>
+struct Equals;
+template<class ArgumentLeft, class ArgumentRight>
+using EqualsPointer = std::unique_ptr<Equals<ArgumentLeft, ArgumentRight>>;
 template<class Argument>
 struct Exists;
 template<class Argument>
@@ -136,8 +140,8 @@ using Terms = std::vector<Term>;
 
 namespace detail
 {
-// TODO: add missing types
 using AtomicFormulaT = Variant<
+	EqualsPointer<Term, Term>,
 	PredicatePointer>;
 }
 
diff --git a/lib/pddl/include/pddl/ASTOutput.h b/lib/pddl/include/pddl/ASTOutput.h
index 0e03a3a..e529738 100644
--- a/lib/pddl/include/pddl/ASTOutput.h
+++ b/lib/pddl/include/pddl/ASTOutput.h
@@ -267,6 +267,14 @@ inline colorlog::ColorStream &print(colorlog::ColorStream &stream, const Either<
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
+template<class ArgumentLeft, class ArgumentRight>
+inline colorlog::ColorStream &print(colorlog::ColorStream &stream, const Equals<ArgumentLeft, ArgumentRight> &equals, pddl::detail::PrintContext &printContext)
+{
+	return print(stream, static_cast<const Binary<Equals<ArgumentLeft, ArgumentRight>, ArgumentLeft, ArgumentRight> &>(equals), printContext);
+}
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
 template<class Argument>
 inline colorlog::ColorStream &print(colorlog::ColorStream &stream, const Exists<Argument> &exists, pddl::detail::PrintContext &printContext)
 {
diff --git a/lib/pddl/include/pddl/detail/normalization/CollectFreeVariables.h b/lib/pddl/include/pddl/detail/normalization/CollectFreeVariables.h
index bbb4951..3234347 100644
--- a/lib/pddl/include/pddl/detail/normalization/CollectFreeVariables.h
+++ b/lib/pddl/include/pddl/detail/normalization/CollectFreeVariables.h
@@ -65,6 +65,15 @@ void collectFreeVariables(const ast::AndPointer<Argument> &and_, std::vector<nor
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
+template<class ArgumentLeft, class ArgumentRight>
+void collectFreeVariables(const ast::EqualsPointer<ArgumentLeft, ArgumentRight> &equals, std::vector<normalizedAST::VariableDeclaration *> &freeVariables, VariableStack &variableStack)
+{
+	collectFreeVariables(equals->argumentLeft, freeVariables, variableStack);
+	collectFreeVariables(equals->argumentRight, freeVariables, variableStack);
+}
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
 template<class Argument>
 void collectFreeVariables(const ast::ExistsPointer<Argument> &exists, std::vector<normalizedAST::VariableDeclaration *> &freeVariables, VariableStack &variableStack)
 {
diff --git a/lib/pddl/src/pddl/detail/normalization/AtomicFormula.cpp b/lib/pddl/src/pddl/detail/normalization/AtomicFormula.cpp
index 91e6c84..6ec1b39 100644
--- a/lib/pddl/src/pddl/detail/normalization/AtomicFormula.cpp
+++ b/lib/pddl/src/pddl/detail/normalization/AtomicFormula.cpp
@@ -17,13 +17,20 @@ namespace detail
 
 normalizedAST::AtomicFormula normalize(ast::AtomicFormula &&atomicFormula)
 {
+	const auto handleEquals =
+		[&](ast::EqualsPointer<ast::Term, ast::Term> &) -> normalizedAST::AtomicFormula
+		{
+			// TODO: implement
+			throw NormalizationException("“=” expressions currently unsupported by normalization");
+		};
+
 	const auto handlePredicate =
 		[&](ast::PredicatePointer &predicate) -> normalizedAST::AtomicFormula
 		{
 			return std::move(predicate);
 		};
 
-	return atomicFormula.match(handlePredicate);
+	return atomicFormula.match(handleEquals, handlePredicate);
 }
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////