diff --git a/Implicit.cpp b/Implicit.cpp
index e69de29..43462df 100644
--- a/Implicit.cpp
+++ b/Implicit.cpp
@@ -0,0 +1,5 @@
+#include "Implicit.hpp"
+
+double ImplicitSurface::operator()(const Point& pt) const {
+    return operator()(pt.x, pt.y, pt.z);
+}
diff --git a/Implicit.hpp b/Implicit.hpp
index b0abfac..ce8264d 100644
--- a/Implicit.hpp
+++ b/Implicit.hpp
@@ -4,8 +4,6 @@
 
 class ImplicitSurface {
     public:
-        virtual double operator() (double x, double y, double z) const;
-        double operator()(const Point& pt) const {
-            return operator()(pt.x, pt.y, pt.z);
-        }
+        virtual double operator() (double x, double y, double z) const = 0;
+        double operator()(const Point& pt) const;
 };