diff --git a/interpreter.rust/Cargo.toml b/interpreter.rust/Cargo.toml
index fc04384..4034bd7 100644
--- a/interpreter.rust/Cargo.toml
+++ b/interpreter.rust/Cargo.toml
@@ -5,6 +5,8 @@ authors = ["Martín Coll <martingonzalezcoll@gmail.com>"]
 edition = "2018"
 
 [dependencies]
+lambda_calculus = "^3.0"
+lambda-calculus-yaml = { path = "./lambda-calculus-yaml" }
 reflection = { path = "./serde-yaml-reflection" }
 risp = "0.7.0"
 risp-yaml = { path = "./risp-yaml" }
@@ -14,6 +16,7 @@ serde_yaml = "0.8"
 
 [workspace]
 members = [
+    "lambda-calculus-yaml",
     "risp-yaml",
     "serde-yaml-reflection",
 ]
diff --git a/interpreter.rust/examples/e0-playground.yaml b/interpreter.rust/examples/e0-playground.yaml
new file mode 100644
index 0000000..39cdd0d
--- /dev/null
+++ b/interpreter.rust/examples/e0-playground.yaml
@@ -0,0 +1 @@
+-
diff --git a/interpreter.rust/examples/e1-scalar.yaml b/interpreter.rust/examples/e1-scalar.yaml
new file mode 100644
index 0000000..0a87dde
--- /dev/null
+++ b/interpreter.rust/examples/e1-scalar.yaml
@@ -0,0 +1,2 @@
+# a scalar
+42
diff --git a/interpreter.rust/examples/e1.yaml b/interpreter.rust/examples/e1.yaml
deleted file mode 100644
index b70d27c..0000000
--- a/interpreter.rust/examples/e1.yaml
+++ /dev/null
@@ -1,2 +0,0 @@
-# 17
-[+, 10, 5, 2]
diff --git a/interpreter.rust/examples/e2.yaml b/interpreter.rust/examples/e2-list.yaml
similarity index 100%
rename from interpreter.rust/examples/e2.yaml
rename to interpreter.rust/examples/e2-list.yaml
diff --git a/interpreter.rust/examples/e3-nested-lists.yaml b/interpreter.rust/examples/e3-nested-lists.yaml
new file mode 100644
index 0000000..6e2bee6
--- /dev/null
+++ b/interpreter.rust/examples/e3-nested-lists.yaml
@@ -0,0 +1,5 @@
+# 19
+- +
+- 10
+- 5
+- [-, 10, 3, 3]
diff --git a/interpreter.rust/examples/e3.yaml b/interpreter.rust/examples/e3.yaml
deleted file mode 100644
index 655df65..0000000
--- a/interpreter.rust/examples/e3.yaml
+++ /dev/null
@@ -1,2 +0,0 @@
-# 19
-[+, 10, 5, [-, 10, 3, 3]]
diff --git a/interpreter.rust/examples/e4-abstraction.yaml b/interpreter.rust/examples/e4-abstraction.yaml
deleted file mode 100644
index c914e76..0000000
--- a/interpreter.rust/examples/e4-abstraction.yaml
+++ /dev/null
@@ -1,8 +0,0 @@
-# 2
-- do
-- a:
-    - +
-    - 1
-    - a
-- - a
-  - 1
diff --git a/interpreter.rust/examples/e4-mapping.yaml b/interpreter.rust/examples/e4-mapping.yaml
new file mode 100644
index 0000000..2fee4dd
--- /dev/null
+++ b/interpreter.rust/examples/e4-mapping.yaml
@@ -0,0 +1,15 @@
+- do
+
+- - def
+  - add-one
+  - x: [+, 1, x]
+
+- - def
+  - add-two
+  - x: [+, 2, x]
+
+# 105
+- - add-one
+  - - add-two
+    - - add-two
+      - 100
diff --git a/interpreter.rust/examples/e5-nested-mapping.yaml b/interpreter.rust/examples/e5-nested-mapping.yaml
new file mode 100644
index 0000000..595c950
--- /dev/null
+++ b/interpreter.rust/examples/e5-nested-mapping.yaml
@@ -0,0 +1,27 @@
+# examples from https://github.com/shybyte/risp
+- do
+
+# ; Define a function
+# (defn double [x] (* x 2))
+- - def
+  - double
+  - x: ['*', x, 2]
+
+# ; Function which returns a function (some call it a closure), which adds x1 to its single argument
+# (defn create_adder [x1]
+#   (fn [x2] (+ x1 x2)))
+- - def
+  - create_adder
+  - x1:
+      x2: [+, x1, x2]
+
+# (def add_20 (create_adder 20))
+- - def
+  - add_20
+  - - create_adder
+    - 20
+
+# 220
+- - add_20
+  - - double
+    - 100
diff --git a/interpreter.rust/lambda-calculus-yaml/Cargo.toml b/interpreter.rust/lambda-calculus-yaml/Cargo.toml
new file mode 100644
index 0000000..b21519e
--- /dev/null
+++ b/interpreter.rust/lambda-calculus-yaml/Cargo.toml
@@ -0,0 +1,12 @@
+[package]
+name = "lambda-calculus-yaml"
+version = "0.1.0"
+authors = ["Martín Coll <martingonzalezcoll@gmail.com>"]
+edition = "2018"
+
+[dependencies]
+lambda_calculus = "^3.0"
+reflection = { path = "../serde-yaml-reflection" }
+serde = { version = "1.0", features = ["derive"] }
+serde_yaml = "0.8"
+serde_test = "1.0.117"
diff --git a/interpreter.rust/lambda-calculus-yaml/src/lib.rs b/interpreter.rust/lambda-calculus-yaml/src/lib.rs
new file mode 100644
index 0000000..3aa99df
--- /dev/null
+++ b/interpreter.rust/lambda-calculus-yaml/src/lib.rs
@@ -0,0 +1,34 @@
+use reflection::Yaml;
+use std::fs::File;
+use std::io::BufReader;
+use lambda_calculus::*;
+use lambda_calculus::data::num::church;
+use std::path::Path;
+
+use std::error::Error;
+
+pub fn read_term_from_file<P: AsRef<Path>>(path: P) -> Result<Yaml, Box<dyn Error>> {
+    let file = File::open(path)?;
+    let reader = BufReader::new(file);
+    Ok(serde_yaml::from_reader(reader)?)
+}
+
+pub fn to_lambda_calculus(yaml_term: &Yaml) -> Term {
+    match yaml_term {
+        Yaml::String(var) => match var.as_ref() {
+            "+" => church::add(),
+            "-" => church::sub(),
+            _ => panic!("variables are numbers because we use de Bruijn notation"),
+        }
+        Yaml::Integer(var) => var.into_church(),
+        // https://www.cs.cornell.edu/courses/cs4110/2018fa/lectures/lecture15.pdf
+        Yaml::Hash(_) => panic!("variables are numbers because we use de Bruijn notation"),
+        Yaml::Array(vec) => match vec.as_slice() {
+            [term] => to_lambda_calculus(term),
+            [lhs, rhs] => app(to_lambda_calculus(lhs), to_lambda_calculus(rhs)),
+            [t0, t1, t2] => app!(to_lambda_calculus(t0), to_lambda_calculus(t1), to_lambda_calculus(t2)),
+            [t0, t1, t2, t3] => app!(to_lambda_calculus(t0), to_lambda_calculus(t1), to_lambda_calculus(t2), to_lambda_calculus(t3)),
+            _ => panic!("unsupported")
+        },
+    }
+}
diff --git a/interpreter.rust/risp-yaml/Cargo.toml b/interpreter.rust/risp-yaml/Cargo.toml
index 274c1ec..c48e56c 100644
--- a/interpreter.rust/risp-yaml/Cargo.toml
+++ b/interpreter.rust/risp-yaml/Cargo.toml
@@ -7,6 +7,7 @@ edition = "2018"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+lambda_calculus = "^3.0"
 reflection = { path = "../serde-yaml-reflection" }
 risp = "0.7"
 serde = { version = "1.0", features = ["derive"] }
diff --git a/interpreter.rust/risp-yaml/src/lib.rs b/interpreter.rust/risp-yaml/src/lib.rs
index e52dfb4..6406b6f 100644
--- a/interpreter.rust/risp-yaml/src/lib.rs
+++ b/interpreter.rust/risp-yaml/src/lib.rs
@@ -1,3 +1,4 @@
+use std::convert::TryInto;
 use reflection::Yaml;
 use risp::types::RispType;
 use std::fs::File;
@@ -15,7 +16,7 @@ pub fn read_term_from_file<P: AsRef<Path>>(path: P) -> Result<Yaml, Box<dyn Erro
 pub fn to_risp(yaml_term: &Yaml) -> RispType {
     match yaml_term {
         Yaml::String(var) => RispType::Symbol(var.to_string()),
-        Yaml::Integer(var) => RispType::Int(*var),
+        Yaml::Integer(var) => RispType::Int((*var).try_into().unwrap()),
         Yaml::Hash(hm) => {
             let (key, val) = hm.iter().next().unwrap();
             RispType::List(vec![
diff --git a/interpreter.rust/serde-yaml-reflection/src/lib.rs b/interpreter.rust/serde-yaml-reflection/src/lib.rs
index ea0cd15..8a2fb12 100644
--- a/interpreter.rust/serde-yaml-reflection/src/lib.rs
+++ b/interpreter.rust/serde-yaml-reflection/src/lib.rs
@@ -6,7 +6,8 @@ use std::collections::HashMap;
 #[derive(Serialize, Deserialize)]
 #[serde(untagged)]
 pub enum Yaml {
-    Integer(i64),
+    Integer(usize),
+    // Integer(i64),
     String(String),
     Array(Vec<Yaml>),
     Hash(HashMap<String, Yaml>),
diff --git a/interpreter.rust/src/bin/eval.rs b/interpreter.rust/src/bin/eval.rs
new file mode 100644
index 0000000..90b6d2c
--- /dev/null
+++ b/interpreter.rust/src/bin/eval.rs
@@ -0,0 +1,12 @@
+use interpreter::eval_file;
+use risp::core::create_core_environment;
+use std::env;
+use std::path::Path;
+
+fn main() {
+    let env = &mut create_core_environment();
+    match env::args().skip(1).next() {
+        Some(path) => eval_file(Path::new(&path), env),
+        None => println!("Usage:\n  cargo run --example eval-file -- [path_to_yaml]"),
+    }
+}
diff --git a/interpreter.rust/src/bin/lambda.rs b/interpreter.rust/src/bin/lambda.rs
new file mode 100644
index 0000000..0a22e18
--- /dev/null
+++ b/interpreter.rust/src/bin/lambda.rs
@@ -0,0 +1,10 @@
+use interpreter::eval_lambda_calculus;
+use std::env;
+use std::path::Path;
+
+fn main() {
+    match env::args().skip(1).next() {
+        Some(path) => eval_lambda_calculus(Path::new(&path)),
+        None => println!("Usage:\n  cargo run --bin lambda -- [path_to_yaml]"),
+    }
+}
diff --git a/interpreter.rust/src/bin/repl.rs b/interpreter.rust/src/bin/repl.rs
new file mode 100644
index 0000000..a64ceda
--- /dev/null
+++ b/interpreter.rust/src/bin/repl.rs
@@ -0,0 +1,20 @@
+use risp::core::create_core_environment;
+use risp::eval::eval;
+use risp_yaml::to_risp;
+use std::io;
+
+fn main() {
+    let env = &mut create_core_environment();
+    loop {
+        println!("risp-yaml >");
+        let mut expr = String::new();
+        while io::stdin().read_line(&mut expr).expect("valid code") > 1 {}
+
+        let yaml_expr = serde_yaml::from_str(&expr).expect("invalid yaml line");
+        let risp_expr = to_risp(&yaml_expr);
+        match eval(risp_expr, env) {
+            Ok(res) => println!("🔥 {:?}", res),
+            Err(e) => println!("🙀 {:?}", e),
+        }
+    }
+}
diff --git a/interpreter.rust/src/lib.rs b/interpreter.rust/src/lib.rs
index aee69c4..3ae7f47 100644
--- a/interpreter.rust/src/lib.rs
+++ b/interpreter.rust/src/lib.rs
@@ -1,3 +1,5 @@
+use lambda_calculus::reduction::*;
+use lambda_calculus_yaml::to_lambda_calculus;
 use risp::environment::Environment;
 use risp::eval::eval;
 use risp_yaml::read_term_from_file;
@@ -13,3 +15,11 @@ pub fn eval_file(path: &Path, env: &mut Environment) {
         Err(e) => println!("// 🙀 => {:?}", e),
     }
 }
+
+pub fn eval_lambda_calculus(path: &Path) {
+    let file = read_term_from_file(path).unwrap();
+
+    let mut expr = to_lambda_calculus(&file);
+    println!("steps: {}", expr.reduce(NOR, 0));
+    println!("{}", expr);
+}
diff --git a/yaml.yaml/data/bool/and.yaml.yaml b/yaml.yaml/data/bool/and.yaml.yaml
index d35d1fb..04305ab 100644
--- a/yaml.yaml/data/bool/and.yaml.yaml
+++ b/yaml.yaml/data/bool/and.yaml.yaml
@@ -1,4 +1,4 @@
-# λp.λq.(p q false)
-- p
-- q
+# λp.λq.(p q false) = λλ.(1 0 false)
+- 1
+- 0
 - false
diff --git a/yaml.yaml/data/bool/yaml.yaml b/yaml.yaml/data/bool/yaml.yaml
index 74859b9..a2b6171 100644
--- a/yaml.yaml/data/bool/yaml.yaml
+++ b/yaml.yaml/data/bool/yaml.yaml
@@ -1,3 +1,6 @@
 # https://users.monash.edu.au/~lloyd/tildeFP/Lambda/Examples/const-bool/
-- true: a
-- false: b
+# and in de Bruijn notation:
+#   true  := λa.λb.a = λλ.1
+#   false := λa.λb.a = λλ.0
+- false
+- true
diff --git a/yaml.yaml/node/term.yaml.yaml b/yaml.yaml/node/term.yaml.yaml
index f6fb94a..639cd30 100644
--- a/yaml.yaml/node/term.yaml.yaml
+++ b/yaml.yaml/node/term.yaml.yaml
@@ -6,6 +6,11 @@
 # also very terse as a general-purpose
 # functional programming language
 
+# https://www.win.tue.nl/automath/archive/pdf/aut029.pdf
+# section 14. ALGORITHMS gave me an idea about the meaning.
+# of mappings and variable names. those are given as free variable
+# lists that carry semantics and are only understood by humans.
+
 scalar: variable
 sequence:
   - mapping: