diff --git a/CMakeLists.txt b/CMakeLists.txt
index 79429ed..a64adf4 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -3,6 +3,14 @@ project(calculator VERSION 1.0 LANGUAGES C)
 
 set(CMAKE_C_STANDARD 11)
 set(CMAKE_C_STANDARD_REQUIRED ON)
+include(FetchContent)
+
+FetchContent_Declare(
+    arena
+    GIT_REPOSITORY https://laentropia-homelab.tail7368da.ts.net/laentropia/Arena.git
+    GIT_TAG main
+    SOURCE_DIR ${CMAKE_SOURCE_DIR}/external/arena
+)
 
 # Export compile_commands.json (para clangd)
 set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
@@ -14,12 +22,29 @@ add_compile_options(
 )
 
 
-include_directories(include)
+FetchContent_MakeAvailable(arena)
+
+add_library(arena STATIC
+    external/arena/src/arena.c
+)
+
+target_include_directories(arena
+    PUBLIC ${CMAKE_SOURCE_DIR}/external/arena/include
+)
 
 add_library(calculator_lib
     src/lexer.c
     src/parser.c
     src/evaluator.c
+    src/ASTNodeArray.c
+)
+
+target_include_directories(calculator_lib
+    PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/include
+)
+
+target_link_libraries(calculator_lib
+    PUBLIC arena
 )
 
 add_executable(calculator src/main.c)
diff --git a/external/arena b/external/arena
new file mode 160000
index 0000000..3d3b859
--- /dev/null
+++ b/external/arena
@@ -0,0 +1 @@
+Subproject commit 3d3b8596ccf2e31983c0c83eb36572a1e4399ec4
diff --git a/include/evaluator.h b/include/evaluator.h
index 78c5730..d176bd2 100644
--- a/include/evaluator.h
+++ b/include/evaluator.h
@@ -2,6 +2,7 @@
 #define EVALUATOR_H
 
 #include "lexer.h"
+#include "arena.h"
 #include <stdint.h>
 
 int64_t evaluate(ASTNode *tree);
diff --git a/include/parser.h b/include/parser.h
index 911d964..03d5443 100644
--- a/include/parser.h
+++ b/include/parser.h
@@ -2,6 +2,7 @@
 #define PARSER_H
 
 #include "lexer.h"
+#include "arena.h"
 #include <stdint.h>
 
 typedef struct {
diff --git a/src/parser.c b/src/parser.c
index c2ac315..6803508 100644
--- a/src/parser.c
+++ b/src/parser.c
@@ -1,9 +1,10 @@
 #include "parser.h"
 #include "lexer.h"
+#include "arena.h"
 #include <stdbool.h>
 #include <stdint.h>
 #include <stdlib.h>
-#include <stdio.h>
+
 
 uint8_t node_lbp(ASTNode node) {
     if (node.type == NODE_INTEGER) {