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docs/tut/crash-course/14-concepts.md

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+# Concepts Summary
+
+A summary of all the concepts covered during the crash course.
+
+## Source
+
+A source of data.
+
+Stores a single value that can be updated.
+
+Created with `source()`.
+
+# Derived Source
+
+A new source composed of other sources.
+
+Created with a plain function or with `derive()`.
+
+## Effect
+
+Anything that happens in response to a source update.
+
+Created with `effect()`.
+
+## Stable Scope
+
+One of the two types of Vide scopes.
+
+Created by:
+
+- `root()`
+- `untrack()`
+- `switch()`
+- `indexes()`
+  
+Stable scopes do not track sources and never rerun.
+
+New stable or reactive scopes can be created within a stable scope.
+
+## Reactive Scope
+
+Created by:
+
+- `effect()`
+- `derive()`
+
+Reactive scopes do track sources and will rerun when those sources update.
+
+New reactive scopes cannot be created within a reactive scope, but stable scopes
+can.
+
+## Scope Owners
+
+A scope created within another scope is *owned* by the other scope, with the
+exception of the scope created by `root()`.
+
+When a scope is rerun or destroyed, all scopes owned by it are automatically
+destroyed.
+
+`root()` creates a stable scope with no owner, instead it is destroyed manually.
+
+## Cleanup
+
+Arbitrary code to run whenever a stable or reactive scope is rerun or destroyed.
+
+Queue a function to run using `cleanup()`.
+
+## Reactive Graph
+
+The combination of stable and reactive scopes can viewed graphically, called a
+*reactive graph*. This can be a more intuitive way to think of the
+relationships between effects and the sources they depend on.
+
+### Code
+
+```lua
+local count = source(0)
+
+root(function()
+    local text = derive(function()
+        return "count: " .. text()
+    end)
+
+    effect(function()
+        print(text())
+    end)
+end)
+```
+
+### Graph resulting from code
+
+```mermaid
+%%{init: {
+    "theme": "base",
+    "themeVariables": {
+        "primaryColor": "#1B1B1F",
+        "primaryTextColor": "#fff",
+        "primaryBorderColor": "#1B1B1F",
+        "lineColor": "#79B8FF",
+        "tertiaryColor": "#161618",
+        "tertiaryBorderColor": "#1C1C1F"
+    }
+}}%%
+
+graph LR
+
+subgraph root
+    text --> effect
+end
+
+count --> text
+```
+
+Notes:
+
+- Since `count` is a source, not an effect, it can exist
+  outside of scopes.
+- An update to `count` will cause `text` to rerun, which
+  then causes `effect` to rerun.
+- When the root scope is destroyed, `text` and
+  `effect` will be destroyed alongside it, since they are
+  owned by it. `count` will be untouched and future updates
+  to `count` will have no effect.