diff --git a/app-proto/full-interface/.gitignore b/app-proto/full-interface/.gitignore
new file mode 100644
index 0000000..19aa86b
--- /dev/null
+++ b/app-proto/full-interface/.gitignore
@@ -0,0 +1,4 @@
+target
+dist
+profiling
+Cargo.lock
\ No newline at end of file
diff --git a/app-proto/sketch-outline/Cargo.toml b/app-proto/full-interface/Cargo.toml
similarity index 98%
rename from app-proto/sketch-outline/Cargo.toml
rename to app-proto/full-interface/Cargo.toml
index 35d199b..920469a 100644
--- a/app-proto/sketch-outline/Cargo.toml
+++ b/app-proto/full-interface/Cargo.toml
@@ -12,6 +12,7 @@ itertools = "0.13.0"
 js-sys = "0.3.70"
 nalgebra = "0.33.0"
 rustc-hash = "2.0.0"
+slab = "0.4.9"
 sycamore = "0.9.0-beta.3"
 
 # The `console_error_panic_hook` crate provides better debugging of panics by
diff --git a/app-proto/sketch-outline/index.html b/app-proto/full-interface/index.html
similarity index 100%
rename from app-proto/sketch-outline/index.html
rename to app-proto/full-interface/index.html
diff --git a/app-proto/full-interface/main.css b/app-proto/full-interface/main.css
new file mode 100644
index 0000000..a687aac
--- /dev/null
+++ b/app-proto/full-interface/main.css
@@ -0,0 +1,120 @@
+body {
+  margin: 0px;
+  color: #fcfcfc;
+  background-color: #222;
+}
+
+/* sidebar */
+
+#sidebar {
+  display: flex;
+  flex-direction: column;
+  float: left;
+  width: 450px;
+  height: 100vh;
+  margin: 0px;
+  padding: 0px;
+  border-width: 0px 1px 0px 0px;
+  border-style: solid;
+  border-color: #555;
+}
+
+/* add-remove */
+
+#add-remove {
+  display: flex;
+  gap: 8px;
+  margin: 8px;
+}
+
+#add-remove > button {
+  width: 32px;
+  height: 32px;
+  font-size: large;
+}
+
+/* outline */
+
+#outline {
+  flex-grow: 1;
+  margin: 0px;
+  padding: 0px;
+  overflow-y: scroll;
+}
+
+li {
+  user-select: none;
+}
+
+summary {
+  display: flex;
+}
+
+summary.selected {
+  color: #fff;
+  background-color: #444;
+}
+
+summary > div, .cst {
+  padding-top: 4px;
+  padding-bottom: 4px;
+}
+
+.elt, .cst {
+  display: flex;
+  flex-grow: 1;
+  padding-left: 8px;
+  padding-right: 8px;
+}
+
+.elt-switch {
+  width: 18px;
+  padding-left: 2px;
+  text-align: center;
+}
+
+details:has(li) .elt-switch::after {
+  content: '▸';
+}
+
+details[open]:has(li) .elt-switch::after {
+  content: '▾';
+}
+
+.elt-label {
+  flex-grow: 1;
+}
+
+.cst-label {
+  flex-grow: 1;
+}
+
+.elt-rep {
+  display: flex;
+}
+
+.elt-rep > div, .cst-rep {
+  padding: 2px 0px 0px 0px;
+  font-size: 10pt;
+  text-align: center;
+  width: 56px;
+}
+
+.cst {
+  font-style: italic;
+}
+
+/* display */
+
+canvas {
+  float: left;
+  margin-left: 20px;
+  margin-top: 20px;
+  background-color: #020202;
+  border: 1px solid #555;
+  border-radius: 16px;
+}
+
+canvas:focus {
+  border-color: #aaa;
+}
\ No newline at end of file
diff --git a/app-proto/full-interface/src/add_remove.rs b/app-proto/full-interface/src/add_remove.rs
new file mode 100644
index 0000000..59220ae
--- /dev/null
+++ b/app-proto/full-interface/src/add_remove.rs
@@ -0,0 +1,55 @@
+use sycamore::prelude::*;
+use web_sys::{MouseEvent, console, wasm_bindgen::JsValue};
+
+use crate::AppState;
+use crate::Constraint;
+
+#[component]
+pub fn AddRemove() -> View {
+    let state = use_context::<AppState>();
+    
+    view! {
+        div(id="add-remove") {
+            button(
+                on:click=move |event: MouseEvent| {
+                    console::log_1(&JsValue::from("constraints:"));
+                    state.assembly.constraints.with(|csts| {
+                        for (_, cst) in csts.into_iter() {
+                            console::log_4(
+                                &JsValue::from(cst.args.0),
+                                &JsValue::from(cst.args.1),
+                                &JsValue::from(":"),
+                                &JsValue::from(cst.rep)
+                            );
+                        }
+                    });
+                }
+            ) { "+" }
+            button(
+                disabled={
+                    state.selection.with(|sel| sel.len() != 2)
+                },
+                on:click=move |event: MouseEvent| {
+                    let args = state.selection.with(
+                        |sel| {
+                            let arg_vec: Vec<_> = sel.into_iter().collect();
+                            (arg_vec[0].clone(), arg_vec[1].clone())
+                        }
+                    );
+                    console::log_5(
+                        &JsValue::from("add constraint"),
+                        &JsValue::from(args.0),
+                        &JsValue::from(args.1),
+                        &JsValue::from(":"),
+                        &JsValue::from(0.0)
+                    );
+                    state.assembly.insert_constraint(Constraint {
+                        args: args,
+                        rep: 0.0
+                    });
+                    state.selection.update(|sel| sel.clear());
+                }
+            ) { "🔗" }
+        }
+    }
+}
\ No newline at end of file
diff --git a/app-proto/full-interface/src/assembly.rs b/app-proto/full-interface/src/assembly.rs
new file mode 100644
index 0000000..6fac59f
--- /dev/null
+++ b/app-proto/full-interface/src/assembly.rs
@@ -0,0 +1,44 @@
+use nalgebra::DVector;
+use rustc_hash::FxHashSet;
+use slab::Slab;
+use sycamore::prelude::*;
+
+#[derive(Clone, PartialEq)]
+pub struct Element {
+    pub id: String,
+    pub label: String,
+    pub color: [f32; 3],
+    pub rep: DVector<f64>,
+    pub constraints: FxHashSet<usize>
+}
+
+#[derive(Clone)]
+pub struct Constraint {
+    pub args: (usize, usize),
+    pub rep: f64
+}
+
+// a complete, view-independent description of an assembly
+#[derive(Clone)]
+pub struct Assembly {
+    pub elements: Signal<Slab<Element>>,
+    pub constraints: Signal<Slab<Constraint>>
+}
+
+impl Assembly {
+    pub fn new() -> Assembly {
+        Assembly {
+            elements: create_signal(Slab::new()),
+            constraints: create_signal(Slab::new())
+        }
+    }
+    
+    pub fn insert_constraint(&self, constraint: Constraint) {
+        let args = constraint.args;
+        let key = self.constraints.update(|csts| csts.insert(constraint));
+        self.elements.update(|elts| {
+            elts[args.0].constraints.insert(key);
+            elts[args.1].constraints.insert(key);
+        })
+    }
+}
\ No newline at end of file
diff --git a/app-proto/sketch-outline/src/display.rs b/app-proto/full-interface/src/display.rs
similarity index 97%
rename from app-proto/sketch-outline/src/display.rs
rename to app-proto/full-interface/src/display.rs
index 2d0900d..52b2ae9 100644
--- a/app-proto/sketch-outline/src/display.rs
+++ b/app-proto/full-interface/src/display.rs
@@ -288,17 +288,17 @@ pub fn Display() -> View {
                 
                 // get the assembly
                 let elements = state.assembly.elements.get_clone();
-                let element_iter = (&elements).values();
-                let reps_world: Vec<_> = element_iter.clone().map(|elt| &assembly_to_world * &elt.rep).collect();
-                let colors: Vec<_> = element_iter.clone().map(|elt|
-                    if state.selection.with(|sel| sel.contains(&elt.id)) {
+                let element_iter = (&elements).into_iter();
+                let reps_world: Vec<_> = element_iter.clone().map(|(_, elt)| &assembly_to_world * &elt.rep).collect();
+                let colors: Vec<_> = element_iter.clone().map(|(key, elt)|
+                    if state.selection.with(|sel| sel.contains(&key)) {
                         elt.color.map(|ch| 0.2 + 0.8*ch)
                     } else {
                         elt.color
                     }
                 ).collect();
-                let highlights: Vec<_> = element_iter.map(|elt|
-                    if state.selection.with(|sel| sel.contains(&elt.id)) {
+                let highlights: Vec<_> = element_iter.map(|(key, _)|
+                    if state.selection.with(|sel| sel.contains(&key)) {
                         1.0_f32
                     } else {
                         HIGHLIGHT
@@ -386,8 +386,8 @@ pub fn Display() -> View {
         // again
         canvas(
             ref=display,
-            width="750",
-            height="750",
+            width="600",
+            height="600",
             tabindex="0",
             on:keydown=move |event: KeyboardEvent| {
                 if event.key() == "Shift" {
diff --git a/app-proto/sketch-outline/src/identity.vert b/app-proto/full-interface/src/identity.vert
similarity index 100%
rename from app-proto/sketch-outline/src/identity.vert
rename to app-proto/full-interface/src/identity.vert
diff --git a/app-proto/sketch-outline/src/inversive.frag b/app-proto/full-interface/src/inversive.frag
similarity index 100%
rename from app-proto/sketch-outline/src/inversive.frag
rename to app-proto/full-interface/src/inversive.frag
diff --git a/app-proto/sketch-outline/src/main.rs b/app-proto/full-interface/src/main.rs
similarity index 61%
rename from app-proto/sketch-outline/src/main.rs
rename to app-proto/full-interface/src/main.rs
index 0d1b0c7..2f31ada 100644
--- a/app-proto/sketch-outline/src/main.rs
+++ b/app-proto/full-interface/src/main.rs
@@ -1,66 +1,79 @@
+mod add_remove;
 mod assembly;
 mod display;
 mod outline;
 
 use nalgebra::DVector;
-use rustc_hash::{FxHashMap, FxHashSet};
+use rustc_hash::FxHashSet;
 use sycamore::prelude::*;
 
-use assembly::{Assembly, Element};
+use add_remove::AddRemove;
+use assembly::{Assembly, Constraint, Element};
 use display::Display;
 use outline::Outline;
 
 #[derive(Clone)]
 struct AppState {
     assembly: Assembly,
-    selection: Signal<FxHashSet<String>>
+    selection: Signal<FxHashSet<usize>>
+}
+
+impl AppState {
+    fn new() -> AppState {
+        AppState {
+            assembly: Assembly::new(),
+            selection: create_signal(FxHashSet::default())
+        }
+    }
 }
 
 fn main() {
     sycamore::render(|| {
-        let state = AppState {
-            assembly: Assembly {
-                elements: create_signal(FxHashMap::default())
-            },
-            selection: create_signal(FxHashSet::default())
-        };
-        state.assembly.elements.update(
+        let state = AppState::new();
+        let key_a = state.assembly.elements.update(
             |elts| elts.insert(
-                "wing_a".to_string(),
                 Element {
                     id: String::from("wing_a"),
                     label: String::from("Wing A"),
                     color: [1.00_f32, 0.25_f32, 0.00_f32],
-                    rep: DVector::<f64>::from_column_slice(&[0.5, 0.5, 0.0, 0.5, -0.25])
+                    rep: DVector::<f64>::from_column_slice(&[0.5, 0.5, 0.0, 0.5, -0.25]),
+                    constraints: FxHashSet::default()
                 }
             )
         );
-        state.assembly.elements.update(
+        let key_b = state.assembly.elements.update(
             |elts| elts.insert(
-                "wing_b".to_string(),
                 Element {
                     id: String::from("wing_b"),
                     label: String::from("Wing B"),
                     color: [0.00_f32, 0.25_f32, 1.00_f32],
-                    rep: DVector::<f64>::from_column_slice(&[-0.5, -0.5, 0.0, 0.5, -0.25])
+                    rep: DVector::<f64>::from_column_slice(&[-0.5, -0.5, 0.0, 0.5, -0.25]),
+                    constraints: FxHashSet::default()
                 },
             )
         );
         state.assembly.elements.update(
             |elts| elts.insert(
-                "central".to_string(),
                 Element {
                     id: String::from("central"),
                     label: String::from("Central"),
                     color: [0.75_f32, 0.75_f32, 0.75_f32],
-                    rep: DVector::<f64>::from_column_slice(&[0.0, 0.0, 0.0, 0.4, -0.625])
+                    rep: DVector::<f64>::from_column_slice(&[0.0, 0.0, 0.0, 0.4, -0.625]),
+                    constraints: FxHashSet::default()
                 }
             )
         );
+        state.assembly.insert_constraint(Constraint {
+            args: (key_a, key_b),
+            rep: 0.5
+        });
         provide_context(state);
         
         view! {
-            Outline {}
+            div(id="sidebar") {
+                AddRemove {}
+                Outline {}
+            }
             Display {}
         }
     });
diff --git a/app-proto/full-interface/src/outline.rs b/app-proto/full-interface/src/outline.rs
new file mode 100644
index 0000000..be5a9b1
--- /dev/null
+++ b/app-proto/full-interface/src/outline.rs
@@ -0,0 +1,155 @@
+use itertools::Itertools;
+use sycamore::{prelude::*, web::tags::div};
+use web_sys::{Element, KeyboardEvent, MouseEvent, wasm_bindgen::JsCast};
+
+use crate::AppState;
+
+// this component lists the elements of the assembly, showing the constraints
+// on each element as a collapsible sub-list. its implementation is based on
+// Kate Morley's HTML + CSS tree views:
+//
+//   https://iamkate.com/code/tree-views/
+//
+#[component]
+pub fn Outline() -> View {
+    // sort the elements alphabetically by ID
+    let elements_sorted = create_memo(|| {
+        let state = use_context::<AppState>();
+        state.assembly.elements
+            .get_clone()
+            .into_iter()
+            .sorted_by_key(|(_, elt)| elt.id.clone())
+            .collect()
+    });
+    
+    view! {
+        ul(
+            id="outline",
+            on:click={
+                let state = use_context::<AppState>();
+                move |_| state.selection.update(|sel| sel.clear())
+            }
+        ) {
+            Keyed(
+                list=elements_sorted,
+                view=|(key, elt)| {
+                    let state = use_context::<AppState>();
+                    let class = create_memo({
+                        move || {
+                            if state.selection.with(|sel| sel.contains(&key)) {
+                                "selected"
+                            } else {
+                                ""
+                            }
+                        }
+                    });
+                    let label = elt.label.clone();
+                    let rep_components = elt.rep.iter().map(|u| {
+                        let u_coord = u.to_string().replace("-", "\u{2212}");
+                        View::from(div().children(u_coord))
+                    }).collect::<Vec<_>>();
+                    let constrained = elt.constraints.len() > 0;
+                    let details_node = create_node_ref();
+                    view! {
+                        /* [TO DO] switch to integer-valued parameters whenever
+                        that becomes possible again */
+                        li {
+                            details(ref=details_node) {
+                                summary(
+                                    class=class.get(),
+                                    on:keydown={
+                                        move |event: KeyboardEvent| {
+                                            match event.key().as_str() {
+                                                "Enter" => {
+                                                    if event.shift_key() {
+                                                        state.selection.update(|sel| {
+                                                            if !sel.remove(&key) {
+                                                                sel.insert(key);
+                                                            }
+                                                        });
+                                                    } else {
+                                                        state.selection.update(|sel| {
+                                                            sel.clear();
+                                                            sel.insert(key);
+                                                        });
+                                                    }
+                                                    event.prevent_default();
+                                                },
+                                                "ArrowRight" if constrained => {
+                                                    let _ = details_node
+                                                        .get()
+                                                        .unchecked_into::<Element>()
+                                                        .set_attribute("open", "");
+                                                },
+                                                "ArrowLeft" => {
+                                                    let _ = details_node
+                                                        .get()
+                                                        .unchecked_into::<Element>()
+                                                        .remove_attribute("open");
+                                                },
+                                                _ => ()
+                                            }
+                                        }
+                                    }
+                                ) {
+                                    div(
+                                        class="elt-switch",
+                                        on:click=|event: MouseEvent| event.stop_propagation()
+                                    )
+                                    div(
+                                        class="elt",
+                                        on:click={
+                                            move |event: MouseEvent| {
+                                                if event.shift_key() {
+                                                    state.selection.update(|sel| {
+                                                        if !sel.remove(&key) {
+                                                            sel.insert(key);
+                                                        }
+                                                    });
+                                                } else {
+                                                    state.selection.update(|sel| {
+                                                        sel.clear();
+                                                        sel.insert(key);
+                                                    });
+                                                }
+                                                event.stop_propagation();
+                                                event.prevent_default();
+                                            }
+                                        }
+                                    ) {
+                                        div(class="elt-label") { (label) }
+                                        div(class="elt-rep") { (rep_components) }
+                                    }
+                                }
+                                ul(class="constraints") {
+                                    Keyed(
+                                        list=elt.constraints.into_iter().collect::<Vec<_>>(),
+                                        view=move |c_key: usize| {
+                                            let c_state = use_context::<AppState>();
+                                            let assembly = &c_state.assembly;
+                                            let cst = assembly.constraints.with(|csts| csts[c_key].clone());
+                                            let other_arg = if cst.args.0 == key {
+                                                cst.args.1
+                                            } else {
+                                                cst.args.0
+                                            };
+                                            let other_arg_label = assembly.elements.with(|elts| elts[other_arg].label.clone());
+                                            view! {
+                                                li(class="cst") {
+                                                    div(class="cst-label") { (other_arg_label) }
+                                                    div(class="cst-rep") { (cst.rep) }
+                                                }
+                                            }
+                                        },
+                                        key=|c_key| c_key.clone()
+                                    )
+                                }
+                            }
+                        }
+                    }
+                },
+                key=|(key, _)| key.clone()
+            )
+        }
+    }
+}
\ No newline at end of file
diff --git a/app-proto/inversive-display/.gitignore b/app-proto/inversive-display/.gitignore
index 238273d..19aa86b 100644
--- a/app-proto/inversive-display/.gitignore
+++ b/app-proto/inversive-display/.gitignore
@@ -1,3 +1,4 @@
 target
 dist
+profiling
 Cargo.lock
\ No newline at end of file
diff --git a/app-proto/sketch-outline/.gitignore b/app-proto/sketch-outline/.gitignore
deleted file mode 100644
index 238273d..0000000
--- a/app-proto/sketch-outline/.gitignore
+++ /dev/null
@@ -1,3 +0,0 @@
-target
-dist
-Cargo.lock
\ No newline at end of file
diff --git a/app-proto/sketch-outline/main.css b/app-proto/sketch-outline/main.css
deleted file mode 100644
index cd7bc44..0000000
--- a/app-proto/sketch-outline/main.css
+++ /dev/null
@@ -1,79 +0,0 @@
-body {
-  margin-left: 20px;
-  margin-top: 20px;
-  color: #fcfcfc;
-  background-color: #222;
-}
-
-/* outline */
-
-ul {
-  float: left;
-  width: 450px;
-  height: 750px;
-  margin: 0px;
-  padding: 8px;
-  border: 1px solid #555;
-  border-radius: 16px;
-  box-sizing: border-box;
-}
-
-li {
-  display: flex;
-  padding: 3px;
-  list-style-type: none;
-  background-color: #444;
-  border-radius: 8px;
-}
-
-li.selected {
-  color: #fff;
-  background-color: #666;
-}
-
-li:not(:last-child) {
-  margin-bottom: 8px;
-}
-
-li > .elt-label {
-  flex-grow: 1;
-  padding: 2px 0px 2px 4px;
-}
-
-li > .elt-rep {
-  display: flex;
-}
-
-li > .elt-rep > div {
-  padding: 2px;
-  margin-left: 3px;
-  text-align: center;
-  width: 60px;
-  background-color: #333;
-}
-
-li.selected > .elt-rep > div {
-  background-color: #555;
-}
-
-li > .elt-rep > div:first-child {
-  border-radius: 6px 0px 0px 6px;
-}
-
-li > .elt-rep > div:last-child {
-  border-radius: 0px 6px 6px 0px;
-}
-
-/* display */
-
-canvas {
-  float: left;
-  margin-left: 16px;
-  background-color: #020202;
-  border: 1px solid #555;
-  border-radius: 16px;
-}
-
-canvas:focus {
-  border-color: #aaa;
-}
\ No newline at end of file
diff --git a/app-proto/sketch-outline/src/assembly.rs b/app-proto/sketch-outline/src/assembly.rs
deleted file mode 100644
index fa7fc3e..0000000
--- a/app-proto/sketch-outline/src/assembly.rs
+++ /dev/null
@@ -1,18 +0,0 @@
-use nalgebra::DVector;
-use rustc_hash::FxHashMap;
-use sycamore::reactive::Signal;
-
-#[derive(Clone, PartialEq)]
-pub struct Element {
-    pub id: String,
-    pub label: String,
-    pub color: [f32; 3],
-    pub rep: DVector<f64>
-}
-
-// a complete, view-independent description of an assembly
-#[derive(Clone)]
-pub struct Assembly {
-    // the order of the elements is arbitrary, and it could change at any time
-    pub elements: Signal<FxHashMap<String, Element>>
-}
\ No newline at end of file
diff --git a/app-proto/sketch-outline/src/outline.rs b/app-proto/sketch-outline/src/outline.rs
deleted file mode 100644
index 13e506e..0000000
--- a/app-proto/sketch-outline/src/outline.rs
+++ /dev/null
@@ -1,80 +0,0 @@
-use itertools::Itertools;
-use sycamore::{prelude::*, web::tags::div};
-use web_sys::KeyboardEvent;
-
-use crate::AppState;
-
-#[component]
-pub fn Outline() -> View {
-    // sort the elements alphabetically by ID
-    let elements_sorted = create_memo(|| {
-        let state = use_context::<AppState>();
-        state.assembly.elements
-            .get_clone()
-            .into_iter()
-            .sorted_by_key(|(id, _)| id.clone())
-            .map(|(_, elt)| elt)
-            .collect()
-    });
-    
-    view! {
-        ul {
-            Keyed(
-                list=elements_sorted,
-                view=|elt| {
-                    let state = use_context::<AppState>();
-                    let class = create_memo({
-                        let id = elt.id.clone();
-                        move || {
-                            if state.selection.with(|sel| sel.contains(&id)) {
-                                "selected"
-                            } else {
-                                ""
-                            }
-                        }
-                    });
-                    let label = elt.label.clone();
-                    let rep_components = elt.rep.iter().map(|u| {
-                        let u_coord = u.to_string().replace("-", "\u{2212}");
-                        View::from(div().children(u_coord))
-                    }).collect::<Vec<_>>();
-                    view! {
-                        /* [TO DO] switch to integer-valued parameters whenever
-                        that becomes possible again */
-                        li(
-                            class=class.get(),
-                            tabindex="0",
-                            on:click={
-                                let id = elt.id.clone();
-                                move |_| {
-                                    state.selection.update(|sel| {
-                                        if !sel.remove(&id) {
-                                            sel.insert(id.clone());
-                                        }
-                                    });
-                                }
-                            },
-                            on:keydown={
-                                let id = elt.id.clone();
-                                move |event: KeyboardEvent| {
-                                    if event.key() == "Enter" {
-                                        state.selection.update(|sel| {
-                                            if !sel.remove(&id) {
-                                                sel.insert(id.clone());
-                                            }
-                                        });
-                                        event.prevent_default();
-                                    }
-                                }
-                            }
-                        ) {
-                            div(class="elt-label") { (label) }
-                            div(class="elt-rep") { (rep_components) }
-                        }
-                    }
-                },
-                key=|elt| elt.id.clone()
-            )
-        }
-    }
-}
\ No newline at end of file