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libs/lib1/CMakeLists.txt

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+# Defines a static library target named 'lib1' from its source file.
+add_library(lib1 STATIC src/lib1.c)
+
+# Specifies include directories that are part of lib1's public interface.
+# - PUBLIC: Means that targets linking to lib1 (like cmake_tutorialApp) will
+#           inherit this include path. This allows them to find lib1.h.
+# ${CMAKE_CURRENT_SOURCE_DIR} refers to the current directory where this CMakeLists.txt resides.
+target_include_directories(lib1 PUBLIC
+    ${CMAKE_CURRENT_SOURCE_DIR}/inc
+)
+
+# Links lib1 to lib2 and lib3.
+# - PRIVATE: Indicates that lib1's implementation depends on lib2 and lib3,
+#            but targets linking to lib1 do NOT need to know about lib2 or lib3.
+# CMake automatically propagates the PUBLIC/INTERFACE include directories from lib2 and lib3
+# to lib1, so explicit include directories for them are not needed here.
+target_link_libraries(lib1 PRIVATE lib2 lib3)

libs/lib1/inc/lib1.h

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+#pragma once
+// No need to include lib2.h or lib3.h here unless their types/functions
+// are part of lib1.h's public interface. For simple calls in lib1.c,
+// including in lib1.c is sufficient.
+
+void lib1_function();

libs/lib1/src/lib1.c

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+#include "lib1.h" // Include lib1's own header
+#include "lib2.h" // Include lib2's header to call lib2_function
+#include "lib3.h" // Include lib3's header to call lib3_function
+#include <stdio.h> // Include standard I/O here, as printf is used in this source file.
+
+void lib1_function() {
+  printf("This is a function from Library 1.\n");
+  lib2_function(); // Call function from lib2
+  lib3_function(); // Call function from lib3
+  printf("Lib1 has called functions from Lib2 and Lib3.\n");
+}