diff --git a/lab01/histogram_internal.h b/lab01/histogram_internal.h
index e69de29..eb9cdfb 100644
--- a/lab01/histogram_internal.h
+++ b/lab01/histogram_internal.h
@@ -0,0 +1,5 @@
+#pragma once
+#include <vector>
+
+void
+find_minmax(const std::vector<double>& numbers, double& min, double& max);