diff --git a/src/runtime/retired/experimental/bits.rs b/src/runtime/retired/experimental/bits.rs
new file mode 100644
index 0000000000000000000000000000000000000000..03166bd28f37e82ebc65c230be5a794f6ae4143e
--- /dev/null
+++ b/src/runtime/retired/experimental/bits.rs
@@ -0,0 +1,457 @@
+use crate::common::*;
+use std::alloc::Layout;
+
+/// Given an iterator over BitChunk Items, iterates over the indices (each represented as a u32) for which the bit is SET,
+/// treating the bits in the BitChunk as a contiguous array.
+/// e.g. input [0b111000, 0b11] gives output [3, 4, 5, 32, 33].
+/// observe that the bits per chunk are ordered from least to most significant bits, yielding smaller to larger usizes.
+/// assumes chunk_iter will yield no more than std::u32::MAX / 32 chunks
+
+pub const fn usize_bytes() -> usize {
+    std::mem::size_of::<usize>()
+}
+pub const fn usize_bits() -> usize {
+    usize_bytes() * 8
+}
+pub const fn usizes_for_bits(bits: usize) -> usize {
+    (bits + (usize_bits() - 1)) / usize_bits()
+}
+
+type Chunk = usize;
+type BitIndex = usize;
+
+pub(crate) struct BitChunkIter<I: Iterator<Item = Chunk>> {
+    cached: usize,
+    chunk_iter: I,
+    next_bit_index: BitIndex,
+}
+impl<I: Iterator<Item = Chunk>> BitChunkIter<I> {
+    pub fn new(chunk_iter: I) -> Self {
+        // first chunk is always a dummy zero, as if chunk_iter yielded Some(FALSE_CHUNK).
+        // Consequences:
+        // 1. our next_bit_index is always off by usize_bits() (we correct for it in Self::next) (no additional overhead)
+        // 2. we cache Chunk and not Option<Chunk>, because chunk_iter.next() is only called in Self::next.
+        Self { chunk_iter, next_bit_index: 0, cached: 0 }
+    }
+}
+impl<I: Iterator<Item = Chunk>> Iterator for BitChunkIter<I> {
+    type Item = BitIndex;
+    fn next(&mut self) -> Option<Self::Item> {
+        let mut chunk = self.cached;
+
+        // loop until either:
+        // 1. there are no more Items to return, or
+        // 2. chunk encodes 1+ Items, one of which we will return.
+        while chunk == 0 {
+            // chunk has no bits set! get the next one...
+            chunk = self.chunk_iter.next()?;
+
+            // ... and jump self.next_bit_index to the next multiple of usize_bits().
+            self.next_bit_index = (self.next_bit_index + usize_bits()) & !(usize_bits() - 1);
+        }
+        // there exists 1+ set bits in chunk
+        // assert(chunk > 0);
+
+        // Until the least significant bit of chunk is 1:
+        // 1. shift chunk to the right,
+        // 2. and increment self.next_bit_index accordingly
+        // effectively performs a little binary search, shifting 32, then 16, ...
+        // TODO perhaps there is a more efficient SIMD op for this?
+        const N_INIT: BitIndex = usize_bits() / 2;
+        let mut n = N_INIT;
+        while n >= 1 {
+            // n is [32,16,8,4,2,1] on 64-bit machine
+            // this loop is unrolled with release optimizations
+            let n_least_significant_mask = (1 << n) - 1;
+            if chunk & n_least_significant_mask == 0 {
+                // no 1 set within 0..n least significant bits.
+                self.next_bit_index += n;
+                chunk >>= n;
+            }
+            n /= 2;
+        }
+        // least significant bit of chunk is 1. Item to return is known.
+        // assert(chunk & 1 == 1)
+
+        // prepare our state for the next time Self::next is called.
+        // Overwrite self.cached such that its shifted state is retained,
+        // and jump over the bit whose index we are about to return.
+        self.next_bit_index += 1;
+        self.cached = chunk >> 1;
+
+        // returned index is usize_bits() smaller than self.next_bit_index because we use an
+        // off-by-usize_bits() encoding to avoid having to cache an Option<usize>.
+        Some(self.next_bit_index - 1 - usize_bits())
+    }
+}
+
+pub(crate) struct BitChunkIterRev<I: ExactSizeIterator<Item = Chunk>> {
+    cached: usize,
+    chunk_iter: I,
+    next_bit_index: BitIndex,
+}
+impl<I: ExactSizeIterator<Item = Chunk>> BitChunkIterRev<I> {
+    pub fn new(chunk_iter: I) -> Self {
+        let next_bit_index = chunk_iter.len() * usize_bits();
+        Self { chunk_iter, next_bit_index, cached: 0 }
+    }
+}
+impl<I: ExactSizeIterator<Item = Chunk>> Iterator for BitChunkIterRev<I> {
+    type Item = BitIndex;
+    fn next(&mut self) -> Option<Self::Item> {
+        let mut chunk = self.cached;
+        if chunk == 0 {
+            self.next_bit_index += usize_bits();
+            loop {
+                self.next_bit_index -= usize_bits();
+                chunk = self.chunk_iter.next()?;
+                if chunk != 0 {
+                    break;
+                }
+            }
+        }
+        const N_INIT: BitIndex = usize_bits() / 2;
+        let mut n = N_INIT;
+        while n >= 1 {
+            let n_most_significant_mask = !0 << (usize_bits() - n);
+            if chunk & n_most_significant_mask == 0 {
+                self.next_bit_index -= n;
+                chunk <<= n;
+            }
+            n /= 2;
+        }
+        self.cached = chunk << 1;
+        self.next_bit_index -= 1;
+        Some(self.next_bit_index)
+    }
+}
+
+/*  --properties-->
+     ___ ___ ___ ___
+    |___|___|___|___|
+  | |___|___|___|___|
+  | |___|___|___|___|
+  | |___|___|___|___|
+  |
+  V
+ entity chunks (groups of size usize_bits())
+*/
+
+// TODO newtypes Entity and Property
+
+#[derive(Debug, Copy, Clone, Eq, PartialEq)]
+pub struct Pair {
+    pub entity: u32,
+    pub property: u32,
+}
+impl From<[u32; 2]> for Pair {
+    fn from([entity, property]: [u32; 2]) -> Self {
+        Pair { entity, property }
+    }
+}
+impl Default for BitMatrix {
+    fn default() -> Self {
+        Self::new(Pair { entity: 0, property: 0 })
+    }
+}
+pub struct BitMatrix {
+    buffer: *mut usize,
+    bounds: Pair,
+    layout: Layout, // layout of the currently-allocated buffer
+}
+impl Drop for BitMatrix {
+    fn drop(&mut self) {
+        unsafe {
+            // ?
+            std::alloc::dealloc(self.buffer as *mut u8, self.layout);
+        }
+    }
+}
+impl Debug for BitMatrix {
+    fn fmt(&self, f: &mut Formatter) -> std::fmt::Result {
+        struct FmtRow<'a> {
+            me: &'a BitMatrix,
+            property: usize,
+        };
+        impl Debug for FmtRow<'_> {
+            fn fmt(&self, f: &mut Formatter) -> std::fmt::Result {
+                let row_chunks = BitMatrix::row_chunks(self.me.bounds.property as usize);
+                let column_chunks = BitMatrix::column_chunks(self.me.bounds.entity as usize);
+                write!(f, "|")?;
+                for entity_chunk in 0..column_chunks {
+                    let mut chunk =
+                        unsafe { *self.me.buffer.add(row_chunks * entity_chunk + self.property) };
+                    let end = if entity_chunk + 1 == column_chunks {
+                        self.me.bounds.entity % usize_bits() as u32
+                    } else {
+                        usize_bits() as u32
+                    };
+                    for _ in 0..end {
+                        let c = match chunk & 1 {
+                            0 => '0',
+                            _ => '1',
+                        };
+                        write!(f, "{}", c)?;
+                        chunk >>= 1;
+                    }
+                    write!(f, "_")?;
+                }
+                Ok(())
+            }
+        }
+        let row_chunks = BitMatrix::row_chunks(self.bounds.property as usize);
+        let iter = (0..row_chunks).map(move |property| FmtRow { me: self, property });
+        f.debug_list().entries(iter).finish()
+    }
+}
+impl BitMatrix {
+    #[inline]
+    const fn row_of(entity: usize) -> usize {
+        entity / usize_bits()
+    }
+    #[inline]
+    const fn row_chunks(property_bound: usize) -> usize {
+        property_bound
+    }
+    #[inline]
+    const fn column_chunks(entity_bound: usize) -> usize {
+        usizes_for_bits(entity_bound)
+    }
+    #[inline]
+    fn offsets_unchecked(&self, at: Pair) -> [usize; 2] {
+        let o_in = at.entity as usize % usize_bits();
+        let row = Self::row_of(at.entity as usize);
+        let row_chunks = self.bounds.property as usize;
+        let o_of = row * row_chunks + at.property as usize;
+        [o_of, o_in]
+    }
+    // returns a u32 which has bits 000...000111...111
+    // for the last JAGGED chunk given the column size
+    // if the last chunk is not jagged (when entity_bound % 32 == 0)
+    // None is returned,
+    // otherwise Some(x) is returned such that x & chunk would mask out
+    // the bits NOT in 0..entity_bound
+    fn last_row_chunk_mask(entity_bound: u32) -> Option<usize> {
+        let zero_prefix_len = entity_bound as usize % usize_bits();
+        if zero_prefix_len == 0 {
+            None
+        } else {
+            Some(!0 >> (usize_bits() - zero_prefix_len))
+        }
+    }
+    fn assert_within_bounds(&self, at: Pair) {
+        assert!(at.entity < self.bounds.entity);
+        assert!(at.property < self.bounds.property);
+    }
+
+    fn layout_for(total_chunks: usize) -> std::alloc::Layout {
+        unsafe {
+            // this layout is ALWAYS valid:
+            // 1. size is always nonzero
+            // 2. size is always a multiple of 4 and 4-aligned
+            Layout::from_size_align_unchecked(usize_bytes() * total_chunks.max(1), usize_bytes())
+        }
+    }
+    /////////
+    pub fn get_bounds(&self) -> &Pair {
+        &self.bounds
+    }
+    pub fn grow_to(&mut self, bounds: Pair) {
+        assert!(bounds.entity >= self.bounds.entity);
+        assert!(bounds.property >= self.bounds.property);
+
+        let old_row_chunks = Self::row_chunks(self.bounds.property as usize);
+        let old_col_chunks = Self::column_chunks(self.bounds.entity as usize);
+        let new_row_chunks = Self::row_chunks(bounds.property as usize);
+        let new_col_chunks = Self::column_chunks(bounds.entity as usize);
+
+        let new_layout = Self::layout_for(new_row_chunks * new_col_chunks);
+        let new_buffer = unsafe {
+            let new_buffer = std::alloc::alloc(new_layout) as *mut usize;
+            let mut src: *mut usize = self.buffer;
+            let mut dest: *mut usize = new_buffer;
+            let row_chunk_diff = new_row_chunks - old_row_chunks;
+            for _col_idx in 0..old_col_chunks {
+                src.copy_to_nonoverlapping(dest, old_row_chunks);
+                src = src.add(old_row_chunks);
+                dest = dest.add(old_row_chunks);
+                if row_chunk_diff > 0 {
+                    dest.write_bytes(0u8, row_chunk_diff);
+                    dest = dest.add(row_chunk_diff);
+                }
+            }
+            let last_zero_chunks = (new_col_chunks - old_col_chunks) * new_row_chunks;
+            dest.write_bytes(0u8, last_zero_chunks);
+            new_buffer
+        };
+        self.layout = new_layout;
+        self.buffer = new_buffer;
+        self.bounds = bounds;
+    }
+    pub fn clear(&mut self) {
+        let total_chunks = Self::row_chunks(self.bounds.property as usize)
+            * Self::column_chunks(self.bounds.entity as usize);
+        unsafe {
+            self.buffer.write_bytes(0u8, total_chunks);
+        }
+    }
+    pub fn new(bounds: Pair) -> Self {
+        let total_chunks = Self::row_chunks(bounds.property as usize)
+            * Self::column_chunks(bounds.entity as usize);
+        let layout = Self::layout_for(total_chunks);
+        let buffer;
+        unsafe {
+            buffer = std::alloc::alloc(layout) as *mut usize;
+            buffer.write_bytes(0u8, total_chunks);
+        };
+        Self { buffer, bounds, layout }
+    }
+    pub fn set(&mut self, at: Pair) {
+        self.assert_within_bounds(at);
+        let [o_of, o_in] = self.offsets_unchecked(at);
+        unsafe { *self.buffer.add(o_of) |= 1 << o_in };
+    }
+    pub fn unset(&mut self, at: Pair) {
+        self.assert_within_bounds(at);
+        let [o_of, o_in] = self.offsets_unchecked(at);
+        unsafe { *self.buffer.add(o_of) &= !(1 << o_in) };
+    }
+    pub fn test(&self, at: Pair) -> bool {
+        self.assert_within_bounds(at);
+        let [o_of, o_in] = self.offsets_unchecked(at);
+        unsafe { *self.buffer.add(o_of) & 1 << o_in != 0 }
+    }
+
+    pub fn batch_mut<'a, 'b>(&mut self, mut chunk_mut_fn: impl FnMut(&'b mut [BitChunk])) {
+        let row_chunks = Self::row_chunks(self.bounds.property as usize);
+        let column_chunks = Self::column_chunks(self.bounds.entity as usize);
+        let mut ptr = self.buffer;
+        for _row in 0..column_chunks {
+            let slice;
+            unsafe {
+                let slicey = std::slice::from_raw_parts_mut(ptr, row_chunks);
+                slice = std::mem::transmute(slicey);
+                ptr = ptr.add(row_chunks);
+            }
+            chunk_mut_fn(slice);
+        }
+        if let Some(mask) = Self::last_row_chunk_mask(self.bounds.entity) {
+            // TODO TEST
+            let mut ptr = unsafe { self.buffer.add((column_chunks - 1) * row_chunks) };
+            for _ in 0..row_chunks {
+                unsafe {
+                    *ptr &= mask;
+                    ptr = ptr.add(1);
+                }
+            }
+        }
+    }
+
+    /// given:
+    /// 1. a buffer to work with
+    /// 2. a _fold function_ for combining the properties of a given entity
+    ///    and returning a new derived property (working )
+    pub fn iter_entities_where<'a, 'b>(
+        &'a self,
+        buf: &'b mut Vec<usize>,
+        mut fold_fn: impl FnMut(&'b [BitChunk]) -> BitChunk,
+    ) -> impl Iterator<Item = u32> + 'b {
+        let buf_start = buf.len();
+        let row_chunks = Self::row_chunks(self.bounds.property as usize);
+        let column_chunks = Self::column_chunks(self.bounds.entity as usize);
+        let mut ptr = self.buffer;
+        for _row in 0..column_chunks {
+            let slice;
+            unsafe {
+                let slicey = std::slice::from_raw_parts(ptr, row_chunks);
+                slice = std::mem::transmute(slicey);
+                ptr = ptr.add(row_chunks);
+            }
+            let chunk = fold_fn(slice);
+            buf.push(chunk.0);
+        }
+        if let Some(mask) = Self::last_row_chunk_mask(self.bounds.entity) {
+            *buf.iter_mut().last().unwrap() &= mask;
+        }
+        BitChunkIter::new(buf.drain(buf_start..)).map(|x| x as u32)
+    }
+    pub fn iter_entities_where_rev<'a, 'b>(
+        &'a self,
+        buf: &'b mut Vec<usize>,
+        mut fold_fn: impl FnMut(&'b [BitChunk]) -> BitChunk,
+    ) -> impl Iterator<Item = u32> + 'b {
+        let buf_start = buf.len();
+        let row_chunks = Self::row_chunks(self.bounds.property as usize);
+        let column_chunks = Self::column_chunks(self.bounds.entity as usize);
+        let mut ptr = self.buffer;
+        for _row in 0..column_chunks {
+            let slice;
+            unsafe {
+                let slicey = std::slice::from_raw_parts(ptr, row_chunks);
+                slice = std::mem::transmute(slicey);
+                ptr = ptr.add(row_chunks);
+            }
+            let chunk = fold_fn(slice);
+            buf.push(chunk.0);
+        }
+        if let Some(mask) = Self::last_row_chunk_mask(self.bounds.entity) {
+            *buf.iter_mut().last().unwrap() &= mask;
+        }
+        BitChunkIterRev::new(buf.drain(buf_start..).rev()).map(|x| x as u32)
+    }
+}
+
+use derive_more::*;
+#[derive(
+    Debug, Copy, Clone, BitAnd, Not, BitOr, BitXor, BitAndAssign, BitOrAssign, BitXorAssign,
+)]
+#[repr(transparent)]
+pub struct BitChunk(usize);
+impl BitChunk {
+    const fn any(self) -> bool {
+        self.0 != FALSE_CHUNK.0
+    }
+    const fn all(self) -> bool {
+        self.0 == TRUE_CHUNK.0
+    }
+}
+pub const TRUE_CHUNK: BitChunk = BitChunk(!0);
+pub const FALSE_CHUNK: BitChunk = BitChunk(0);
+
+#[test]
+fn matrix_test() {
+    let mut m = BitMatrix::new(Pair { entity: 70, property: 3 });
+    m.set([2, 0].into());
+    m.set([40, 1].into());
+    m.set([40, 2].into());
+    m.set([40, 0].into());
+    println!("{:#?}", &m);
+
+    m.batch_mut(|p| p[0] = TRUE_CHUNK);
+    println!("{:#?}", &m);
+
+    for i in (0..40).step_by(7) {
+        m.unset([i, 0].into());
+    }
+    m.unset([62, 0].into());
+    println!("{:#?}", &m);
+
+    m.batch_mut(move |p| p[1] = p[0] ^ TRUE_CHUNK);
+    println!("{:#?}", &m);
+
+    let mut buf = vec![];
+    for index in m.iter_entities_where(&mut buf, move |p| p[1]) {
+        println!("index {}", index);
+    }
+    for index in m.iter_entities_where_rev(&mut buf, move |p| p[1]) {
+        println!("index {}", index);
+    }
+}
+
+#[test]
+fn bit_chunk_iter_rev() {
+    let x = &[0b1, 0b1000011, 0, 0, 0b101];
+    for i in BitChunkIterRev::new(x.iter().copied()) {
+        println!("i = {:?}", i);
+    }
+}