About Penluma

Penluma - pen + lumen, the light of the pen - is a growing library of 536 deep-dive notes across 28 topics, from staff-level system design and distributed systems to economics, clear thinking, and money. Every topic is written to take you from plain-language intuition, to precise mechanics, to the failure modes that show up in the real world.

Unlike most online write-ups, these aren't cheat sheets. They include back-of-the-envelope math, worked examples, comparison tables, war stories, and test-yourself questions. They're meant to be read slowly and worked through - the version I wish I'd had when I was learning each of these things.

The problem I'm trying to solve

Most explanations sit at one of two extremes. Cheat sheets and hot takes are easy to read but too shallow to use - you finish them knowing about a topic without actually understanding it. Textbooks and papers are rigorous but so dense that most people bounce off before the idea ever clicks. Both leave you stranded the moment you hit a real problem.

Penluma aims for the missing middle: writing that is genuinely deep but still readable - rigorous where it counts, plain-language where it can be.

The method: every topic, three levels deep

Each deep-dive is built to move through three layers, in order:

1. Intuition - the plain-language mental model first, the way a smart friend would explain it before any jargon shows up.
2. Mechanics - precisely how the thing actually works, step by step. No hand-waving, no "it just works."
3. Failure modes - where it breaks in the real world, why, and what to do about it. This is the part most explanations skip, and it's usually the part that matters.

What you'll find here

The library spans 28 topics grouped into a handful of areas. It keeps growing as I work through new material:

• AI & LLMs - 3 topics
• Certifications - 1 topic
• Communication - 2 topics
• Engineering - 6 topics
• Essays - 1 topic
• Money & Business - 6 topics
• Thinking & Decisions - 9 topics

Who this is for

Penluma is for the curious builder, operator, or student who would rather understand something properly than skim ten summaries of it - engineers levelling up toward staff, founders trying to reason about their own business, and anyone who likes chasing an idea all the way to the bottom. If you want a quick answer to copy-paste, this probably isn't the place. If you want to actually get it, welcome.

How to get the most out of it

• Read slowly. These are worked through, not skimmed - treat them like a short chapter, not a tweet.
• Do the math and the test-yourself questions instead of nodding past them; that's where understanding actually sticks.
• Follow a numbered series start to finish - the ordering is deliberate, each part builds on the last.

Who writes this

I'm Brexis Wazik - an engineer and a compulsive learner. Penluma is my habit of taking one hard topic at a time and writing through it until the fog clears, then publishing the part that survived. There's no team and no ghostwriters: one voice, working things out in the open, so the next person learning the same thing gets there faster.

What makes it different

• Depth over volume - one topic fully worked through beats ten skimmed for the algorithm.
• Evergreen, not news - the residue that stays true in five years, not a take that expires next week.
• Open by default - the whole library is free. No paywall, no signup wall to read.

Stay in the loop

New deep-dives get added over time. If you'd like to know when a substantial new topic or post lands, subscribe using the form at the bottom of the page - one email when there's something worth reading, and nothing else.