diff --git a/labs/04/README.md b/labs/04/README.md
index 43d601d..4d5bd81 100644
--- a/labs/04/README.md
+++ b/labs/04/README.md
@@ -1,27 +1,49 @@
-# Lab 04 instructions
+# Activity 3.1: Lexical Analyzer (SCANNER)
 
-## Objective
+Author: Emilio Berber Maldonado A01640603
 
-Make the student understand the power of lex language making a C code that
-performs the lexical analysis of the ac src program
+## Purpose
+The objective of this activity is to develop a basic lexical analyzer (scanner) using Flex. This analyzer processes a source code file and outputs the corresponding tokens, recognizing keywords, identifiers, numbers, operators, unknown digits and cooments.
 
-# Requirements
+## Requirements
+- Install Flex (Fast Lexical Analyzer Generator)
+- Install GCC or another C compiler
+- Unix-like environment or terminal (Linux, macOS, or Git Bash/MSYS2 for Windows)
 
-* Linux machine, either a VM or a bare metal host
-* GCC compiler (at least version 4.8)
-* lex compiler
-* Autotools
-* git send mail server installed and configured on your Linux machine
+## Files
+- `lex_analaizer.l`: The Flex definition file containing the lexical rules
+- `example.ac`: Sample input file with code to analyze
+- `lex_analyzer.exe`: Compiled executable generated from the `.l` file (on Windows)
+- lex.yy.c
 
-## Instructions
+## How to Compile and Run
 
-Please generate a LEX code to parse the previous example of lab 03.
+1. Generate the C source from the `.l` file:
+   ```bash
+   flex lex_analaizer.l
+   ```
 
-A valid line of code in ac could be:
+2. Compile the generated `lex.yy.c` file:
+   ```bash
+   gcc lex.yy.c -o lex_analyzer
+   ```
 
+3. Run the analyzer with your test input:
+   ```bash
+   ./lex_analyzer example.ac
+   ```
+## Output Format
+Each recognized token is printed to standard output on a separate line. Comments and unknown characters are also reported as `COMMENT` and `UNKNOWN`, respectively. Whitespace and line breaks are ignored in tokenization but respected in output formatting for clarity.
+
+## Example
+
+### Input: (`example.ac`)
 ```
+a =    3
+// Emilio Berber
+// Mi matrícula es: A01640603
+h = 123131312321312
 // basic code
-
 //float b
 f b
 
@@ -29,18 +51,22 @@ f b
 i a
 
 // a = 5
-a = 5
+a =           5
 
 // b = a + 3.2
 b = a + 3.2
 
-//print 8.5
-p b
+// print 8.5
+p 8.5
+?
 ```
 
-Your output should be
-
+### Output:
 ```
+id assign inum
+COMMENT
+COMMENT
+id assign inum
 COMMENT
 COMMENT
 floatdcl id
@@ -51,45 +77,20 @@ id assign inum
 COMMENT
 id assign id plus fnum
 COMMENT
-print id
-```
-
-## Expected result:
-
-* Code a lex_analaizer.L that fulfill the requirements
-* Generate a random AC code with:
-
-```
-python3 code_generator.py > example.ac
-
+print fnum
+UNKNOWN
 ```
 
-* Compile your code with the makefile and execute as follows:
-
-```
-./lex_analaizer example.ac
-```
-
-
-## Please send the mail as PR:
-
-```
-    $ git add lex_analaizer.l
-    $ git commit -s -m <STUDENT-ID>-homework-04
-```
-Do some tests sending the mail to your personal account, if you get the mail,
-then you can be sure I will get the mail
-
-## Good links for Hints
-
-* [lextutorial](https://ds9a.nl/lex-yacc/cvs/lex-yacc-howto.html)
-* [lex & yacc Second
-Edition](https://www.amazon.com/lex-yacc-Doug-Brown/dp/1565920007)
-At the end of chapter 1 there is a very similar code as the one requested in
-this homework, you just need to read chapter 1 of this book :)
-* [useoflexinc](https://www.quora.com/What-is-the-function-of-yylex-yyin-yyout-and-fclose-yyout-in-LEX)
-
-## Time to do the homework:
-
-One week from the moment the mail is sent to students
-
+## Recognized Tokens
+| Token      | Description                        |
+|------------|------------------------------------|
+| `floatdcl` | Float declaration (`f`)            |
+| `intdcl`   | Integer declaration (`i`)          |
+| `print`    | Print statement (`p`)              |
+| `id`       | Identifier (variable name)         |
+| `assign`   | Assignment operator (`=`)          |
+| `plus`     | Addition operator (`+`)            |
+| `inum`     | Integer number                     |
+| `fnum`     | Floating point number              |
+| `COMMENT`  | Line comment (starts with `//`)    |
+| `UNKNOWN`  | Any unrecognized symbol (e.g., `?`)|
\ No newline at end of file
diff --git a/labs/04/example.ac b/labs/04/example.ac
new file mode 100644
index 0000000..2735c8b
--- /dev/null
+++ b/labs/04/example.ac
@@ -0,0 +1,25 @@
+a =    3
+// Emilio Berber
+// Mi matrícula es: A01640603
+h = 123131312321312
+// basic code
+//float b
+f b
+
+
+
+// integer a
+i a
+
+// a = 5
+a =           5
+
+// b = a + 3.2
+b = a + 3.2
+
+// print 8.5
+p 8.5
+
+?
+
+
diff --git a/labs/04/lex_analaizer.l b/labs/04/lex_analaizer.l
new file mode 100644
index 0000000..5090371
--- /dev/null
+++ b/labs/04/lex_analaizer.l
@@ -0,0 +1,39 @@
+%{
+#include <stdio.h>
+%}
+
+
+%%
+
+\/\/.*              { printf("COMMENT\n"); }
+"f"                 { printf("floatdcl "); }
+"i"                 { printf("intdcl "); }
+"p"                 { printf("print "); }
+"="                 { printf("assign ");}
+"+"                 { printf("plus ");}
+[0-9]+              { printf("inum \n");}
+[0-9]*"."[0-9]+     { printf("fnum \n"); }
+[a-zA-Z]+           { printf("id ");}
+[ \t\n]+            /* ignore whitespace and line breaks */;
+.                   { printf("UNKNOWN \n"); } 
+
+
+%%
+
+
+int main(int argc, char *argv[]) {
+    if (argc > 1) {
+        FILE *file = fopen(argv[1], "r");
+        if (!file) {
+            perror("Error to open the file");
+            return 1;
+        }
+        yyin = file;  // Flex
+    }
+    yylex();
+    return 0;
+}
+
+int yywrap() {
+    return 1;
+}