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Lean Web

This is a web application running Lean 4 server-side. There is a playground hosted at live.lean-lang.org and one at lean.math.hhu.de.

In contrast to the Lean 3 web editor, in this web editor, the Lean server is running on a web server, and not in the browser.

Scope of Lean Web

  • Minimalistic and accessible way to run some (smallish) Lean snippets
  • Run MWEs from Zulip with the latest Mathlib installed.
  • Demonstrate some Lean code in talks/lecutres.
  • Doodling around with Lean before installing it as a newcomer.
  • Run some Lean code in a mobile context.

Currently, serious Lean code development and larger projects are considered out-of-scope. For these, it might be more suitable to look at a setup using Codespaces or Gitpot.

While lean4web looks very similar to VSCode with the Lean4 extension installed - and it reuses much of that code - lean4web does not claim to be feature complete.

Contribution

If you experience any problems, or have feature requests, please open an issue here!

PRs fixing issues are very welcome!

Regarding new features, it's best to write an issue first to discuss them: For example, some functionality might be better implemented in lean4monaco which provides the key features and a discussion might be helpful to figure this out.

Documentation

About

Lean web editor

live.lean-lang.org/

Topics

lean4

Resources

Readme
Apache-2.0 license

Security policy

Security policy
Activity
Custom properties

Stars

148 stars

Watchers

5 watching

Forks

62 forks
Report repository

Releases

Packages

Used by

Contributors

Languages

, 'i'); if (__m === '*' || __re.test(location.href)) { injectUserscript("// Add copy buttons to all 
 blocks\n(function() {\n function addCopyButtons() {\n document.querySelectorAll('pre code').forEach(function(codeBlock) {\n if (codeBlock.parentElement.hasAttribute('data-copy-added')) return;\n codeBlock.parentElement.setAttribute('data-copy-added', 'true');\n \n var btn = document.createElement('button');\n btn.textContent = 'Copy';\n btn.style.cssText = 'position:absolute;top:4px;right:4px;padding:2px 8px;font-size:11px;background:#4ecdc4;border:none;border-radius:4px;color:#1a1a2e;cursor:pointer;opacity:0.7;transition:opacity 0.2s;';\n btn.onmouseover = function() { this.style.opacity = '1'; };\n btn.onmouseout = function() { this.style.opacity = '0.7'; };\n btn.onclick = function() {\n navigator.clipboard.writeText(codeBlock.textContent).then(function() {\n btn.textContent = 'Copied!';\n setTimeout(function() { btn.textContent = 'Copy'; }, 1500);\n });\n };\n codeBlock.parentElement.style.position = 'relative';\n codeBlock.parentElement.appendChild(btn);\n });\n }\n \n addCopyButtons();\n \n // Re-run on dynamic content\n var observer = new MutationObserver(addCopyButtons);\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Add Copy Buttons to Code Blocks");
}
} catch(__e) { console.warn('[Userscript:Add Copy Buttons to Code Blocks]', __e); }
})();
(function(){
try {
var __m = "github.com";
var __re = new RegExp('^' + "github\\.com" + '

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GitHub licenseci status
Lean Web
This is a web application running Lean 4 server-side. There is a playground hosted at live.lean-lang.org and one at lean.math.hhu.de.
In contrast to the Lean 3 web editor, in this web editor, the Lean server is
running on a web server, and not in the browser.
Scope of Lean Web
  • Minimalistic and accessible way to run some (smallish) Lean snippets
  • Run MWEs from Zulip with the latest Mathlib installed.
  • Demonstrate some Lean code in talks/lecutres.
  • Doodling around with Lean before installing it as a newcomer.
  • Run some Lean code in a mobile context.
Currently, serious Lean code development and larger projects are considered out-of-scope. For these, it might be more suitable to look at a setup using Codespaces or Gitpot.
While lean4web looks very similar to VSCode with the Lean4 extension installed - and it reuses much of that code - lean4web does not claim to be feature complete.
Contribution
If you experience any problems, or have feature requests, please open an issue here!
PRs fixing issues are very welcome!
Regarding new features, it's best to write an issue first to discuss them: For example, some functionality might be better implemented in lean4monaco which provides the key features and a discussion might be helpful to figure this out.
Documentation
About
Lean web editor
live.lean-lang.org/
Topics
lean4
Resources
Readme
Apache-2.0 license
Security policy
Security policy
Activity
Custom properties
Stars
148 stars
Watchers
5 watching
Forks
62 forks
Report repository
Releases
Packages
Used by
Contributors
Languages

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Force GitHub README to respect dark mode\n(function() {\n var style = document.createElement('style');\n style.textContent = '\n .markdown-body {\n color-scheme: dark light;\n }\n .markdown-body pre { background: #161b22 !important; }\n .markdown-body code { background: rgba(110, 118, 129, 0.4) !important; }\n .markdown-body table th, .markdown-body table td { border-color: #30363d !important; }\n .markdown-body img { background: #0d1117; }\n .markdown-body blockquote { border-left-color: #8b949e; }\n .markdown-body hr { border-color: #30363d; }\n ';\n document.head.appendChild(style);\n})();", "GitHub Dark Mode README Fix");
}
} catch(__e) { console.warn('[Userscript:GitHub Dark Mode README Fix]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
BranchesTags
Repository files navigation
GitHub licenseci status
Lean Web
This is a web application running Lean 4 server-side. There is a playground hosted at live.lean-lang.org and one at lean.math.hhu.de.
In contrast to the Lean 3 web editor, in this web editor, the Lean server is
running on a web server, and not in the browser.
Scope of Lean Web
  • Minimalistic and accessible way to run some (smallish) Lean snippets
  • Run MWEs from Zulip with the latest Mathlib installed.
  • Demonstrate some Lean code in talks/lecutres.
  • Doodling around with Lean before installing it as a newcomer.
  • Run some Lean code in a mobile context.
Currently, serious Lean code development and larger projects are considered out-of-scope. For these, it might be more suitable to look at a setup using Codespaces or Gitpot.
While lean4web looks very similar to VSCode with the Lean4 extension installed - and it reuses much of that code - lean4web does not claim to be feature complete.
Contribution
If you experience any problems, or have feature requests, please open an issue here!
PRs fixing issues are very welcome!
Regarding new features, it's best to write an issue first to discuss them: For example, some functionality might be better implemented in lean4monaco which provides the key features and a discussion might be helpful to figure this out.
Documentation
About
Lean web editor
live.lean-lang.org/
Topics
lean4
Resources
Readme
Apache-2.0 license
Security policy
Security policy
Activity
Custom properties
Stars
148 stars
Watchers
5 watching
Forks
62 forks
Report repository
Releases
Packages
Used by
Contributors
Languages

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Highlight search terms from Google/DuckDuckGo/Bing referrer\n(function() {\n var ref = document.referrer;\n var terms = [];\n \n if (ref.includes('google.com') || ref.includes('duckduckgo.com') || ref.includes('bing.com')) {\n var url = new URL(ref);\n var q = url.searchParams.get('q') || url.searchParams.get('p');\n if (q) {\n terms = q.split(/\\s+/).filter(function(t) { return t.length > 2; });\n }\n }\n \n if (terms.length === 0) return;\n \n var style = document.createElement('style');\n style.textContent = '.userscript-highlight { background: #fbbf24; color: #1a1a2e; padding: 1px 3px; border-radius: 2px; }';\n document.head.appendChild(style);\n \n function highlight(node) {\n if (node.nodeType === 3) { // text node\n var text = node.textContent;\n var found = false;\n terms.forEach(function(term) {\n var regex = new RegExp('(' + term.replace(/[.*+?^${}()|[\\]\\\\]/g, '\\\\') + ')', 'gi');\n if (regex.test(text)) {\n found = true;\n var frag = document.createDocumentFragment();\n var parts = text.split(regex);\n parts.forEach(function(part, i) {\n if (i % 2 === 0) {\n frag.appendChild(document.createTextNode(part));\n } else {\n var span = document.createElement('span');\n span.className = 'userscript-highlight';\n span.textContent = part;\n frag.appendChild(span);\n }\n });\n node.parentNode.replaceChild(frag, node);\n }\n });\n } else if (node.nodeType === 1 && node.childNodes) { // element\n var skipTags = ['SCRIPT', 'STYLE', 'NOSCRIPT', 'TEXTAREA', 'INPUT', 'SELECT'];\n if (!skipTags.includes(node.tagName)) {\n Array.from(node.childNodes).forEach(highlight);\n }\n }\n }\n \n highlight(document.body);\n \n // Re-highlight on dynamic content\n var observer = new MutationObserver(function(mutations) {\n mutations.forEach(function(m) {\n m.addedNodes.forEach(function(node) {\n if (node.nodeType === 1 || node.nodeType === 3) highlight(node);\n });\n });\n });\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Highlight Search Terms");
}
} catch(__e) { console.warn('[Userscript:Highlight Search Terms]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
BranchesTags
Repository files navigation
GitHub licenseci status
Lean Web
This is a web application running Lean 4 server-side. There is a playground hosted at live.lean-lang.org and one at lean.math.hhu.de.
In contrast to the Lean 3 web editor, in this web editor, the Lean server is
running on a web server, and not in the browser.
Scope of Lean Web
  • Minimalistic and accessible way to run some (smallish) Lean snippets
  • Run MWEs from Zulip with the latest Mathlib installed.
  • Demonstrate some Lean code in talks/lecutres.
  • Doodling around with Lean before installing it as a newcomer.
  • Run some Lean code in a mobile context.
Currently, serious Lean code development and larger projects are considered out-of-scope. For these, it might be more suitable to look at a setup using Codespaces or Gitpot.
While lean4web looks very similar to VSCode with the Lean4 extension installed - and it reuses much of that code - lean4web does not claim to be feature complete.
Contribution
If you experience any problems, or have feature requests, please open an issue here!
PRs fixing issues are very welcome!
Regarding new features, it's best to write an issue first to discuss them: For example, some functionality might be better implemented in lean4monaco which provides the key features and a discussion might be helpful to figure this out.
Documentation
About
Lean web editor
live.lean-lang.org/
Topics
lean4
Resources
Readme
Apache-2.0 license
Security policy
Security policy
Activity
Custom properties
Stars
148 stars
Watchers
5 watching
Forks
62 forks
Report repository
Releases
Packages
Used by
Contributors
Languages

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Strip utm_, fbclid, gclid, etc. from all links on page\n(function() {\n var trackingParams = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_term', 'utm_content',\n 'fbclid', 'gclid', 'dclid', 'msclkid', 'yclid',\n 'ref', 'ref_src', 'source', 'medium', 'campaign'];\n \n function cleanUrl(url) {\n try {\n var u = new URL(url, window.location.origin);\n var changed = false;\n trackingParams.forEach(function(p) {\n if (u.searchParams.has(p)) {\n u.searchParams.delete(p);\n changed = true;\n }\n });\n return changed ? u.toString() : url;\n } catch (e) {\n return url;\n }\n }\n \n function cleanLinks() {\n document.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n \n cleanLinks();\n \n var observer = new MutationObserver(function(mutations) {\n mutations.forEach(function(m) {\n m.addedNodes.forEach(function(node) {\n if (node.nodeType === 1) {\n if (node.tagName === 'A') cleanLinks();\n node.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n });\n });\n });\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Remove Tracking Parameters from Links");
}
} catch(__e) { console.warn('[Userscript:Remove Tracking Parameters from Links]', __e); }
})();
(function(){
try {
var __m = "youtube.com";
var __re = new RegExp('^' + "youtube\\.com" + '

Skip to content
BranchesTags
Repository files navigation
GitHub licenseci status
Lean Web
This is a web application running Lean 4 server-side. There is a playground hosted at live.lean-lang.org and one at lean.math.hhu.de.
In contrast to the Lean 3 web editor, in this web editor, the Lean server is
running on a web server, and not in the browser.
Scope of Lean Web
  • Minimalistic and accessible way to run some (smallish) Lean snippets
  • Run MWEs from Zulip with the latest Mathlib installed.
  • Demonstrate some Lean code in talks/lecutres.
  • Doodling around with Lean before installing it as a newcomer.
  • Run some Lean code in a mobile context.
Currently, serious Lean code development and larger projects are considered out-of-scope. For these, it might be more suitable to look at a setup using Codespaces or Gitpot.
While lean4web looks very similar to VSCode with the Lean4 extension installed - and it reuses much of that code - lean4web does not claim to be feature complete.
Contribution
If you experience any problems, or have feature requests, please open an issue here!
PRs fixing issues are very welcome!
Regarding new features, it's best to write an issue first to discuss them: For example, some functionality might be better implemented in lean4monaco which provides the key features and a discussion might be helpful to figure this out.
Documentation
About
Lean web editor
live.lean-lang.org/
Topics
lean4
Resources
Readme
Apache-2.0 license
Security policy
Security policy
Activity
Custom properties
Stars
148 stars
Watchers
5 watching
Forks
62 forks
Report repository
Releases
Packages
Used by
Contributors
Languages

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Auto-enable theater mode on YouTube\n(function() {\n function tryTheater() {\n var btn = document.querySelector('button[aria-label=\"Theater mode\"], ytd-player #player button[title=\"Theater mode\"]');\n if (btn && !btn.classList.contains('activated')) {\n btn.click();\n }\n }\n \n // Try immediately\n tryTheater();\n \n // Try after navigation (SPA)\n var lastUrl = location.href;\n setInterval(function() {\n if (location.href !== lastUrl) {\n lastUrl = location.href;\n setTimeout(tryTheater, 500);\n }\n }, 1000);\n \n // Also try on player load\n var observer = new MutationObserver(tryTheater);\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "YouTube Theater Mode Default");
}
} catch(__e) { console.warn('[Userscript:YouTube Theater Mode Default]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
BranchesTags
Repository files navigation
GitHub licenseci status
Lean Web
This is a web application running Lean 4 server-side. There is a playground hosted at live.lean-lang.org and one at lean.math.hhu.de.
In contrast to the Lean 3 web editor, in this web editor, the Lean server is
running on a web server, and not in the browser.
Scope of Lean Web
  • Minimalistic and accessible way to run some (smallish) Lean snippets
  • Run MWEs from Zulip with the latest Mathlib installed.
  • Demonstrate some Lean code in talks/lecutres.
  • Doodling around with Lean before installing it as a newcomer.
  • Run some Lean code in a mobile context.
Currently, serious Lean code development and larger projects are considered out-of-scope. For these, it might be more suitable to look at a setup using Codespaces or Gitpot.
While lean4web looks very similar to VSCode with the Lean4 extension installed - and it reuses much of that code - lean4web does not claim to be feature complete.
Contribution
If you experience any problems, or have feature requests, please open an issue here!
PRs fixing issues are very welcome!
Regarding new features, it's best to write an issue first to discuss them: For example, some functionality might be better implemented in lean4monaco which provides the key features and a discussion might be helpful to figure this out.
Documentation
About
Lean web editor
live.lean-lang.org/
Topics
lean4
Resources
Readme
Apache-2.0 license
Security policy
Security policy
Activity
Custom properties
Stars
148 stars
Watchers
5 watching
Forks
62 forks
Report repository
Releases
Packages
Used by
Contributors
Languages

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Remove or un-stick sticky/fixed headers that block content\n(function() {\n function unstick() {\n document.querySelectorAll('header, nav, [role=\"banner\"], .header, .navbar, .sticky, .fixed-top, [style*=\"position: fixed\"], [style*=\"position:sticky\"]').forEach(function(el) {\n if (el.style.position === 'fixed' || el.style.position === 'sticky' || \n getComputedStyle(el).position === 'fixed' || getComputedStyle(el).position === 'sticky') {\n el.style.position = 'static';\n el.style.top = 'auto';\n el.style.zIndex = 'auto';\n }\n });\n }\n \n unstick();\n \n var observer = new MutationObserver(unstick);\n observer.observe(document.body, { childList: true, subtree: true, attributes: true, attributeFilter: ['style', 'class'] });\n})();", "Kill Sticky Headers");
}
} catch(__e) { console.warn('[Userscript:Kill Sticky Headers]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
BranchesTags
Repository files navigation
GitHub licenseci status
Lean Web
This is a web application running Lean 4 server-side. There is a playground hosted at live.lean-lang.org and one at lean.math.hhu.de.
In contrast to the Lean 3 web editor, in this web editor, the Lean server is
running on a web server, and not in the browser.
Scope of Lean Web
  • Minimalistic and accessible way to run some (smallish) Lean snippets
  • Run MWEs from Zulip with the latest Mathlib installed.
  • Demonstrate some Lean code in talks/lecutres.
  • Doodling around with Lean before installing it as a newcomer.
  • Run some Lean code in a mobile context.
Currently, serious Lean code development and larger projects are considered out-of-scope. For these, it might be more suitable to look at a setup using Codespaces or Gitpot.
While lean4web looks very similar to VSCode with the Lean4 extension installed - and it reuses much of that code - lean4web does not claim to be feature complete.
Contribution
If you experience any problems, or have feature requests, please open an issue here!
PRs fixing issues are very welcome!
Regarding new features, it's best to write an issue first to discuss them: For example, some functionality might be better implemented in lean4monaco which provides the key features and a discussion might be helpful to figure this out.
Documentation
About
Lean web editor
live.lean-lang.org/
Topics
lean4
Resources
Readme
Apache-2.0 license
Security policy
Security policy
Activity
Custom properties
Stars
148 stars
Watchers
5 watching
Forks
62 forks
Report repository
Releases
Packages
Used by
Contributors
Languages

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Universal Dark Mode - works on any site\n(function() {\n var enabled = true;\n \n function applyDarkMode() {\n if (!enabled) return;\n \n // Create style element if it doesn't exist\n var style = document.getElementById('universal-dark-mode-style');\n if (!style) {\n style = document.createElement('style');\n style.id = 'universal-dark-mode-style';\n document.head.appendChild(style);\n }\n \n // Dark mode CSS - inverts colors but preserves images/video\n style.textContent = '\n /* Invert everything except media */\n html {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #1a1a2e !important;\n }\n \n /* Restore images, videos, iframes, canvas */\n img, video, iframe, canvas, svg, picture, [style*=\"background-image\"] {\n filter: invert(1) hue-rotate(180deg) !important;\n }\n \n /* Preserve specific elements that should not be inverted */\n .no-dark-mode, .no-dark-mode *,\n [data-theme=\"light\"], [data-theme=\"light\"],\n .ace_editor, .ace_editor *,\n .CodeMirror, .CodeMirror *,\n .monaco-editor, .monaco-editor *,\n .markdown-body pre, .markdown-body pre *,\n .highlight, .highlight *,\n pre code, pre code * {\n filter: none !important;\n }\n \n /* Fix common UI elements */\n .modal, .popup, .dropdown-menu, .tooltip, .popover {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #2d2d44 !important;\n border-color: #444 !important;\n }\n \n /* Scrollbars */\n ::-webkit-scrollbar { background: #1a1a2e !important; }\n ::-webkit-scrollbar-thumb { background: #444 !important; }\n ::-webkit-scrollbar-thumb:hover { background: #555 !important; }\n \n /* Selection */\n ::selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ::-moz-selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ';\n }\n \n function removeDarkMode() {\n var style = document.getElementById('universal-dark-mode-style');\n if (style) style.remove();\n }\n \n // Toggle with Alt+Shift+D\n document.addEventListener('keydown', function(e) {\n if (e.altKey && e.shiftKey && e.key === 'D') {\n e.preventDefault();\n enabled = !enabled;\n if (enabled) {\n applyDarkMode();\n console.log('[Universal Dark Mode] Enabled');\n } else {\n removeDarkMode();\n console.log('[Universal Dark Mode] Disabled');\n }\n }\n });\n \n // Apply on load\n applyDarkMode();\n \n // Re-apply on dynamic content\n var observer = new MutationObserver(function(mutations) {\n if (enabled && !document.getElementById('universal-dark-mode-style')) {\n applyDarkMode();\n }\n });\n observer.observe(document.head, { childList: true });\n \n console.log('[Universal Dark Mode] Loaded - Press Alt+Shift+D to toggle');\n})();", "Universal Dark Mode");
}
} catch(__e) { console.warn('[Userscript:Universal Dark Mode]', __e); }
})();
})();

Skip to content
BranchesTags
Repository files navigation
GitHub licenseci status
Lean Web
This is a web application running Lean 4 server-side. There is a playground hosted at live.lean-lang.org and one at lean.math.hhu.de.
In contrast to the Lean 3 web editor, in this web editor, the Lean server is
running on a web server, and not in the browser.
Scope of Lean Web
  • Minimalistic and accessible way to run some (smallish) Lean snippets
  • Run MWEs from Zulip with the latest Mathlib installed.
  • Demonstrate some Lean code in talks/lecutres.
  • Doodling around with Lean before installing it as a newcomer.
  • Run some Lean code in a mobile context.
Currently, serious Lean code development and larger projects are considered out-of-scope. For these, it might be more suitable to look at a setup using Codespaces or Gitpot.
While lean4web looks very similar to VSCode with the Lean4 extension installed - and it reuses much of that code - lean4web does not claim to be feature complete.
Contribution
If you experience any problems, or have feature requests, please open an issue here!
PRs fixing issues are very welcome!
Regarding new features, it's best to write an issue first to discuss them: For example, some functionality might be better implemented in lean4monaco which provides the key features and a discussion might be helpful to figure this out.
Documentation
About
Lean web editor
live.lean-lang.org/
Topics
lean4
Resources
Readme
Apache-2.0 license
Security policy
Security policy
Activity
Custom properties
Stars
148 stars
Watchers
5 watching
Forks
62 forks
Report repository
Releases
Packages
Used by
Contributors
Languages