diff --git a/math/fib/Cargo.toml b/math/fib/Cargo.toml
new file mode 100644
index 0000000..7f4efbb
--- /dev/null
+++ b/math/fib/Cargo.toml
@@ -0,0 +1,9 @@
+[package]
+name = "fib"
+version = "0.1.0"
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+nested = { path = "../../nested" }
diff --git a/math/fib/src/main.rs b/math/fib/src/main.rs
new file mode 100644
index 0000000..ac3d1bc
--- /dev/null
+++ b/math/fib/src/main.rs
@@ -0,0 +1,58 @@
+
+use std::{
+    fs::File,
+    io::{Read, Write},
+    os::unix::io::FromRawFd
+};
+
+fn fib(n: u64) -> u64 {
+    let mut y = 0;
+    let mut y1 = 1;
+    let mut y2 = 0;
+
+    for _ in 0 .. n {
+        y = y1 + y2;
+        y2 = y1;
+        y1 = y;
+    }
+
+    y
+}
+
+fn main() {
+    nested::magic_header();
+
+    eprintln!("            Fibonacci Sequence");
+
+    nested::magic_header();
+
+    eprintln!("
+interface (Sequence ℕ) 0 1");
+
+    let mut f0 = unsafe { File::from_raw_fd(0) };
+    eprintln!("
+> 0: n
+  ( ℕ )
+  ( MachineInt )
+  ( MachineWord )
+  ( Pipe Shot MachineWord )
+");
+
+    let mut f1 = unsafe { File::from_raw_fd(1) };
+    eprintln!("
+< 1: n'th fibonacci number
+  ( ℕ )
+  ( MachineInt )
+  ( MachineWord )
+  ( Pipe Shot MachineWord )
+");
+
+    nested::magic_header();
+
+    let mut bytes = [0 as u8; 8];
+    f0.read_exact(&mut bytes);
+    let n = u64::from_le_bytes(bytes);
+    bytes = fib(n).to_le_bytes();
+    f1.write(&bytes);
+}
+
diff --git a/math/int2str/Cargo.toml b/math/int2str/Cargo.toml
new file mode 100644
index 0000000..cdac039
--- /dev/null
+++ b/math/int2str/Cargo.toml
@@ -0,0 +1,9 @@
+[package]
+name = "int2str"
+version = "0.1.0"
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+nested = { path = "../../nested" }
diff --git a/math/int2str/src/main.rs b/math/int2str/src/main.rs
new file mode 100644
index 0000000..db2b19a
--- /dev/null
+++ b/math/int2str/src/main.rs
@@ -0,0 +1,38 @@
+
+use std::{
+    fs::File,
+    io::{Read, Write},
+    os::unix::io::FromRawFd
+};
+
+fn main() {
+    nested::magic_header();
+    eprintln!("     Human-readably Print MachineInt");
+    nested::magic_header();
+
+    let mut f0 = unsafe { File::from_raw_fd(0) };
+    eprintln!("
+> 0:
+  ( ℕ )
+  ( MachineInt )
+  ( MachineWord )
+  ( Array 8 MachineSlab )
+  ( Pipe Shot (Array 8 MachineSlab) )
+");
+
+    eprintln!("
+< 1:
+  ( ℕ )
+  ( Sequence (Digit 10) )
+  ( Sequence ASCII )
+  ( Sequence MachineSlab )
+  ( Pipe Shot (Sequence MachineSlab) )
+");
+
+    nested::magic_header();
+
+    let mut bytes = [0 as u8; 8];
+    f0.read_exact(&mut bytes);
+    println!("{}", u64::from_le_bytes(bytes));
+}
+
diff --git a/math/str2int/Cargo.toml b/math/str2int/Cargo.toml
new file mode 100644
index 0000000..b85bed6
--- /dev/null
+++ b/math/str2int/Cargo.toml
@@ -0,0 +1,9 @@
+[package]
+name = "str2int"
+version = "0.1.0"
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+nested = { path = "../../nested" }
diff --git a/math/str2int/src/main.rs b/math/str2int/src/main.rs
new file mode 100644
index 0000000..596004c
--- /dev/null
+++ b/math/str2int/src/main.rs
@@ -0,0 +1,40 @@
+
+use std::{
+    fs::File,
+    io::{Read, Write},
+    os::unix::io::FromRawFd
+};
+
+fn main() {
+    nested::magic_header();
+    eprintln!("       Parse MachineInt from String");
+    nested::magic_header();
+
+    let mut f0 = unsafe { File::from_raw_fd(0) };
+    eprintln!("
+> 0:
+  ( ℕ )
+  ( Sequence (Digit 10) )
+  ( Sequence ASCII )
+  ( Sequence MachineSlab )
+  ( Pipe Shot (Sequence MachineSlab) )
+");
+
+    let mut f1 = unsafe { File::from_raw_fd(1) };
+    eprintln!("
+< 1:
+  ( ℕ )
+  ( MachineInt )
+  ( MachineWord )
+  ( Array 8 MachineSlab )
+  ( Pipe Shot (Array 8 MachineSlab) )
+");
+
+    nested::magic_header();
+
+    let mut chars = Vec::new();
+    f0.read_to_end(&mut chars);
+    chars.retain(|c| (*c as char).is_numeric());
+    f1.write(&u64::from_str_radix(&String::from_utf8_lossy(&chars), 10).unwrap().to_le_bytes());
+}
+