diff --git a/Cargo.toml b/Cargo.toml
index c442cab..00261ad 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -5,5 +5,6 @@ members = [
     "terminal/ansi_parser",
     "math/str2int",
     "math/int2str",
+    "math/radix_transform",
     "math/fib"
 ]
diff --git a/math/radix_transform/Cargo.toml b/math/radix_transform/Cargo.toml
new file mode 100644
index 0000000..678a012
--- /dev/null
+++ b/math/radix_transform/Cargo.toml
@@ -0,0 +1,13 @@
+[package]
+name = "radix_transform"
+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" }
+
+[dependencies.async-std]
+version = "1.9.0"
+features = ["unstable", "attributes"]
diff --git a/math/radix_transform/src/main.rs b/math/radix_transform/src/main.rs
new file mode 100644
index 0000000..1440884
--- /dev/null
+++ b/math/radix_transform/src/main.rs
@@ -0,0 +1,105 @@
+
+use {
+    std::sync::{Arc, RwLock},
+    nested::{
+        core::{
+            View,
+            ViewPort,
+            Observer,
+            ObserverBroadcast,
+            InnerViewPort,
+            OuterViewPort
+        },
+        sequence::{SequenceView, VecBuffer},
+        integer::{RadixProjection}
+    }
+};
+
+#[async_std::main]
+async fn main() {
+    nested::magic_header();
+    eprintln!("    Convert Radix of Positional Integer");
+    nested::magic_header();
+
+    let mut args = std::env::args();
+    args.next().expect("Arg $0 missing!");
+
+    eprintln!("
+$1: src_radix
+  ( ℕ )
+  ( PositionalInt 10 LittleEndian )
+  ( Sequence (Digit 10) )
+  ( Sequence Ascii )
+  ( ArgString )
+");
+    let src_radix_str = args.next().expect("Arg $1 required!");
+
+    
+    eprintln!("
+$2: dst_radix
+  ( ℕ )
+  ( PositionalInt 10 LittleEndian )
+  ( Sequence (Digit 10) )
+  ( Sequence Ascii )
+  ( ArgString )
+");
+    let dst_radix_str = args.next().expect("Arg $2 required!");
+    
+    eprintln!("
+>0: n
+  ( ℕ ) ~~ <1
+  ( PositionalInt src_radix LittleEndian )
+  ( Sequence (Digit src_radix) )
+  ( Sequence MachineInt )
+  ( PipeStream bincode (SequenceDiff MachineInt) )
+");
+
+    eprintln!("
+<1: n
+  ( ℕ ) ~~ >0
+  ( PositionalInt dst_radix LittleEndian )
+  ( Sequence (Digit dst_radix) )
+  ( Sequence MachineInt )
+  ( PipeStream bincode (SequenceDiff MachineInt) )
+");
+
+    nested::magic_header();
+
+    let src_radix = usize::from_str_radix(&src_radix_str, 10).expect("could not parse src_radix");
+    let dst_radix = usize::from_str_radix(&dst_radix_str, 10).expect("could not parse dst_radix");
+
+    let src_digits_port = ViewPort::new();
+    let dst_digits_port = ViewPort::new();
+
+    let mut src_digits = VecBuffer::<usize>::new(src_digits_port.inner());
+
+    let proj = RadixProjection::new(
+        src_radix,
+        dst_radix,
+        src_digits_port.outer().to_sequence(),
+        dst_digits_port.inner()
+    );
+
+    // output dst digits
+    let writer = {
+        use std::{
+            fs::File,
+            io::{Read, Write},
+            os::unix::io::FromRawFd
+        };
+
+        dst_digits_port.outer().serialize_json(unsafe { std::fs::File::from_raw_fd(1) })
+    };
+
+    // start reading src digits
+    {
+        use async_std::{
+            fs::File,
+            io::{Read, Write},
+            os::unix::io::FromRawFd
+        };
+
+        src_digits.from_json(unsafe { async_std::fs::File::from_raw_fd(0) }).await;
+    }
+}
+
diff --git a/nested/src/integer/add.rs b/nested/src/integer/add.rs
new file mode 100644
index 0000000..9ba42d4
--- /dev/null
+++ b/nested/src/integer/add.rs
@@ -0,0 +1,75 @@
+use {
+    std::sync::{Arc, RwLock},
+    crate::{
+        core::{InnerViewPort, OuterViewPort, ObserverBroadcast},
+        sequence::{SequenceView, VecBuffer},
+        projection::ProjectionHelper
+    }
+};
+
+fn posint_add(
+    radix: usize,
+    a: impl SequenceView<Item = usize>,
+    b: impl SequenceView<Item = usize>
+) -> Vec<usize> {
+    let mut carry = 0;
+    let mut result = Vec::new();
+
+    for digit_idx in 0 .. std::cmp::max(a.len().unwrap_or(0), b.len().unwrap_or(0)) {
+        let sum =
+            a.get(&digit_idx).unwrap_or(0) +
+            b.get(&digit_idx).unwrap_or(0) +
+            carry;
+
+        result.push(sum % radix);
+
+        carry =
+            if sum > radix {
+                sum - radix
+            } else {
+                0
+            };
+    }
+
+    if carry > 0 {
+        result.push(carry);
+    }
+
+    result
+}
+
+pub struct Add {
+    radix: usize,
+    a: Arc<dyn SequenceView<Item = usize>>, // PosInt, Little Endian
+    b: Arc<dyn SequenceView<Item = usize>>, // PosInt, Little Endian
+    c: VecBuffer<usize>,
+    proj_helper: ProjectionHelper<Self>
+}
+
+impl Add {
+    pub fn new(
+        radix: usize,
+        a: OuterViewPort<dyn SequenceView<Item = usize>>,
+        b: OuterViewPort<dyn SequenceView<Item = usize>>,
+        c: InnerViewPort<RwLock<Vec<usize>>>//<dyn SequenceView<Item = usize>>
+    ) -> Arc<RwLock<Self>> {
+        let mut proj_helper = ProjectionHelper::new();
+        let add = Arc::new(RwLock::new(
+            Add {
+                radix,
+                a: proj_helper.new_sequence_arg(a, |s: &mut Self, _digit_idx| s.update()),
+                b: proj_helper.new_sequence_arg(b, |s: &mut Self, _digit_idx| s.update()),
+                c: VecBuffer::new(c),
+                proj_helper
+            }
+        ));
+        add
+    }
+
+    fn update(&mut self) {
+        self.c.clear();
+        for digit in posint_add(self.radix, self.a.clone(), self.b.clone()) {
+            self.c.push(digit);
+        }
+    }
+}
diff --git a/nested/src/integer/mod.rs b/nested/src/integer/mod.rs
new file mode 100644
index 0000000..1c122f8
--- /dev/null
+++ b/nested/src/integer/mod.rs
@@ -0,0 +1,9 @@
+
+pub mod radix;
+pub mod add;
+
+pub use {
+    radix::RadixProjection,
+    add::Add
+};
+
diff --git a/nested/src/integer/radix.rs b/nested/src/integer/radix.rs
new file mode 100644
index 0000000..a62876f
--- /dev/null
+++ b/nested/src/integer/radix.rs
@@ -0,0 +1,99 @@
+use {
+    std::sync::{Arc, RwLock},
+    crate::{
+        core::{
+            View,
+            ViewPort,
+            Observer,
+            ObserverBroadcast,
+            InnerViewPort,
+            OuterViewPort
+        },
+        sequence::{SequenceView, VecBuffer}
+    }
+};
+
+pub struct RadixProjection {
+    src_radix: usize,
+    dst_radix: usize,
+    src_digits: Option<Arc<dyn SequenceView<Item = usize>>>,
+    dst_digits: RwLock<VecBuffer<usize>>
+}
+
+impl RadixProjection {
+    pub fn new(
+        src_radix: usize,
+        dst_radix: usize,
+        src_digits: OuterViewPort<dyn SequenceView<Item = usize>>,
+        dst_digits: InnerViewPort<RwLock<Vec<usize>>>
+    ) -> Arc<RwLock<Self>> {
+        let proj = Arc::new(RwLock::new(
+            RadixProjection {
+                src_radix,
+                dst_radix,
+                src_digits: None,
+                dst_digits: RwLock::new(VecBuffer::new(dst_digits))
+            }
+        ));
+        src_digits.add_observer(proj.clone());
+        proj
+    }
+
+    fn machine_int(&self) -> usize {
+        let mut val = 0;
+        let mut r = 1;
+        for i in 0 .. self.src_digits.len().unwrap_or(0) {
+            val += r * self.src_digits.get(&i).unwrap();
+            r *= self.src_radix;
+        }
+
+        val
+    }
+
+    // recalculate everything
+    fn update(&self) {
+        let mut dst = self.dst_digits.write().unwrap();
+        dst.clear();
+
+        let mut val = self.machine_int();
+
+        while val > 0 {
+            dst.push(val % self.dst_radix);
+            val /= self.dst_radix;
+        }        
+    }
+
+    fn update_dst_digit(&mut self, idx: usize) {
+        /*
+        let v = 0; // calculate new digit value
+
+        // which src-digits are responsible?
+
+        if idx < self.dst_digits.len() {
+            self.dst_digits.get_mut(idx) = v;
+        } else if idx == self.dst_digits.len() {
+            self.dst_digits.push(v);
+        } else {
+            // error
+        }
+*/
+    }
+}
+
+impl Observer<dyn SequenceView<Item = usize>> for RadixProjection {
+    fn reset(&mut self, view: Option<Arc<dyn SequenceView<Item = usize>>>) {
+        eprintln!("reset");
+
+        self.src_digits = view;
+    }
+
+    fn notify(&self, idx: &usize) {
+        // todo:
+        // src digit i changed.
+        // which dst-digits does it affect?
+        // update dst-digit j:
+
+        // ...but for now the easy way
+        self.update();
+    }
+}
diff --git a/nested/src/lib.rs b/nested/src/lib.rs
index abee199..6d65631 100644
--- a/nested/src/lib.rs
+++ b/nested/src/lib.rs
@@ -1,39 +1,18 @@
 #![feature(trait_alias)]
 
 pub mod core;
+pub mod projection;
+
+pub mod singleton;
 pub mod index;
 pub mod grid;
 pub mod sequence;
-pub mod singleton;
 pub mod terminal;
-pub mod projection;
+pub mod integer;
+
 pub mod string_editor;
 pub mod leveled_term_view;
 
-/* maybe?
-pub use {
-    cgmath::{Vector2, Point2},
-    termion::event::{Event, Key},
-    crate::{
-        core::{View, Observer, ObserverExt, ObserverBroadcast, ViewPort, OuterViewPort},
-        index::{ImplIndexView},
-        terminal::{
-            TerminalView,
-            TerminalAtom,
-            TerminalStyle,
-            TerminalEvent,
-            Terminal,
-            TerminalCompositor
-        },
-        sequence::{VecBuffer, SequenceView},
-        grid::{GridOffset, GridWindowIterator},
-        singleton::{SingletonView, SingletonBuffer},
-        string_editor::{StringEditor, insert_view::StringInsertView},
-        leveled_term_view::LeveledTermView
-    }
-};
- */
-
 pub fn magic_header() {
     eprintln!("<<<<>>>><<>><><<>><<<*>>><<>><><<>><<<<>>>>");
 }