diff --git a/core/src/main/java/it/cavallium/warppi/math/rules/dsl/VisitorPattern.java b/core/src/main/java/it/cavallium/warppi/math/rules/dsl/VisitorPattern.java
new file mode 100644
index 00000000..f698799d
--- /dev/null
+++ b/core/src/main/java/it/cavallium/warppi/math/rules/dsl/VisitorPattern.java
@@ -0,0 +1,184 @@
+package it.cavallium.warppi.math.rules.dsl;
+
+import it.cavallium.warppi.math.Function;
+import it.cavallium.warppi.math.FunctionVisitor;
+import it.cavallium.warppi.math.functions.*;
+import it.cavallium.warppi.math.functions.Number;
+import it.cavallium.warppi.math.functions.equations.Equation;
+import it.cavallium.warppi.math.functions.equations.EquationsSystem;
+import it.cavallium.warppi.math.functions.equations.EquationsSystemPart;
+import it.cavallium.warppi.math.functions.trigonometry.*;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Optional;
+
+/**
+ * A <code>Pattern</code> which implements <code>match</code> as a visitor.
+ */
+public abstract class VisitorPattern implements Pattern, FunctionVisitor<Optional<Map<String, Function>>> {
+    @Override
+    public Optional<Map<String, Function>> match(Function function) {
+        return function.accept(this);
+    }
+
+    /**
+     * Gathers captured sub-functions from two matches, checking for equality
+     * of ones with the same name.
+     *
+     * @param match1 Sub-functions from one match.
+     * @param match2 Sub-functions from the other match.
+     * @return A <code>Map</code> containing all sub-functions, or an empty
+     *         <code>Optional</code> if the same name is used to refer to
+     *         non-equal sub-functions in the two matches.
+     */
+    protected Optional<Map<String, Function>> mergeMatches(
+            Map<String, Function> match1,
+            Map<String, Function> match2
+    ) {
+        if (!checkSubFunctionEquality(match1, match2)) {
+            return Optional.empty();
+        }
+
+        Map<String, Function> merged = new HashMap<>();
+        merged.putAll(match1);
+        merged.putAll(match2);
+        return Optional.of(merged);
+    }
+
+    private boolean checkSubFunctionEquality(Map<String, Function> match1, Map<String, Function> match2) {
+        for (Map.Entry<String, Function> leftSubFunction : match1.entrySet()) {
+            final String key = leftSubFunction.getKey();
+            if (match2.containsKey(key)
+                    && !match2.get(key).equals(leftSubFunction.getValue())) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    @Override
+    public Optional<Map<String, Function>> visit(ArcCosine arcCosine) {
+        return Optional.empty();
+    }
+
+    @Override
+    public Optional<Map<String, Function>> visit(ArcSine arcSine) {
+        return Optional.empty();
+    }
+
+    @Override
+    public Optional<Map<String, Function>> visit(ArcTangent arcTangent) {
+        return Optional.empty();
+    }
+
+    @Override
+    public Optional<Map<String, Function>> visit(Cosine cosine) {
+        return Optional.empty();
+    }
+
+    @Override
+    public Optional<Map<String, Function>> visit(Division division) {
+        return Optional.empty();
+    }
+
+    @Override
+    public Optional<Map<String, Function>> visit(EmptyNumber emptyNumber) {
+        return Optional.empty();
+    }
+
+    @Override
+    public Optional<Map<String, Function>> visit(Equation equation) {
+        return Optional.empty();
+    }
+
+    @Override
+    public Optional<Map<String, Function>> visit(EquationsSystem equationsSystem) {
+        return Optional.empty();
+    }
+
+    @Override
+    public Optional<Map<String, Function>> visit(EquationsSystemPart equationsSystemPart) {
+        return Optional.empty();
+    }
+
+    @Override
+    public Optional<Map<String, Function>> visit(Expression expression) {
+        return Optional.empty();
+    }
+
+    @Override
+    public Optional<Map<String, Function>> visit(Joke joke) {
+        return Optional.empty();
+    }
+
+    @Override
+    public Optional<Map<String, Function>> visit(Logarithm logarithm) {
+        return Optional.empty();
+    }
+
+    @Override
+    public Optional<Map<String, Function>> visit(Multiplication multiplication) {
+        return Optional.empty();
+    }
+
+    @Override
+    public Optional<Map<String, Function>> visit(Negative negative) {
+        return Optional.empty();
+    }
+
+    @Override
+    public Optional<Map<String, Function>> visit(Number number) {
+        return Optional.empty();
+    }
+
+    @Override
+    public Optional<Map<String, Function>> visit(Power power) {
+        return Optional.empty();
+    }
+
+    @Override
+    public Optional<Map<String, Function>> visit(Root root) {
+        return Optional.empty();
+    }
+
+    @Override
+    public Optional<Map<String, Function>> visit(RootSquare rootSquare) {
+        return Optional.empty();
+    }
+
+    @Override
+    public Optional<Map<String, Function>> visit(Sine sine) {
+        return Optional.empty();
+    }
+
+    @Override
+    public Optional<Map<String, Function>> visit(Subtraction subtraction) {
+        return Optional.empty();
+    }
+
+    @Override
+    public Optional<Map<String, Function>> visit(SumSubtraction sumSubtraction) {
+        return Optional.empty();
+    }
+
+    @Override
+    public Optional<Map<String, Function>> visit(Sum sum) {
+        return Optional.empty();
+    }
+
+    @Override
+    public Optional<Map<String, Function>> visit(Tangent tangent) {
+        return Optional.empty();
+    }
+
+    @Override
+    public Optional<Map<String, Function>> visit(Undefined undefined) {
+        return Optional.empty();
+    }
+
+    @Override
+    public Optional<Map<String, Function>> visit(Variable variable) {
+        return Optional.empty();
+    }
+}