Set math (notations and P iff Q)

Some math basics for trying to understand and/or MIT’s OCW on math for computer science.


for set A and B

∪ = union, Everything in A AND everything in B (including overlap)
∩ = intersection, Everything in A AND B (just the overlap)
A \ B = {x | x ∈ A and x ∈ B} = Everything in A but not in B

A ∈ B = A is part of B (smaller side of ∈ towards the smaller set)
Q.E.D. = Proof done (normally a block symbol, but wordpres….)
P iff Q = P if and only if Q = P ↔ Q) = P implies Q and vice-versa

∩ intersection (wikipedia)

Set proof (both statements imply eachother)

With set A,B,C:

A ∩ (B ∪ C) = (A ∩ B) ∪ (A ∩ C)
the intersection of A with (B andor C)
(The intersection between A and B) andor (the intersection between A and C)

This looks correct, but let’s prove it.

We show that z ∈ A ∩ (B ∪ C) implies that
z ∈ (A ∩ B) ∪ (A ∩ C) and vice-versa.

First, we show that z ∈ A ∩ (B ∪ C) implies that
z ∈ (A ∩ B) ∪ (A ∩ C):

Assume that z ∈ A ∩ (B ∪ C).
Then z is in A and z is also in B or C. Thus, z is in
either A∩B or A∩C, which implies z ∈ (A∩B)∪(A∩C)


Now, we show that z ∈ (A∩B)∪(A∩C) implies that
z ∈ A ∩ (B ∪ C).

Assume that z ∈ (A ∩ B) ∪ (A ∩ C).
Then z is in both A and B or else z is in both A and
C. Thus, z is in A and z is also in B or C. This implies
that z ∈ A ∩ (B ∪ C).


Proof by contradiction

Proof by contra-positive ((P → Q) ↔ (¬Q → ¬P) is a tautology. )

In order to prove a proposition P by contradiction:

  1. Write, “We use proof by contradiction.”
  2. Write, “Suppose P is false.”
  3. Deduce a logical contradiction.
  4. Write, “This is a contradiction. Therefore, P must
    be true.”

Theorem: sqrt(2) is irrational

proving something irrational is hard, so instead assume it to be rational:

sqrt(2) = a/b (in the lowest terms a and b possible)
2 = (a^2)/(b^2)
a^2 = 2(b^2)
which means a^2 is even
thus a is even
thus a^2 is a multiple of 4
thus b^2 is a multiple of 4
thus b is also even

a and b are even which is a contradiction with the lowest term rule
thus a/b is not rational

Be a decent client / seller

The rant of my life. Someone wants to sell you something that they’ve created, loved and cared for.

Please be decent customer. This seller (hopefully) isn’t just here to take your money. They have something you need and are happy to give it to you.

This also works the opposite way. Be a good seller.
We are in this world together, for whoever’s sake please don’t just apply shitty tricks from the book to get more money. What is your goal in life? I hope happiness. Do those 20 extra bucks make you happier? Yes, maybe. But does that add up to a constant feeling of happiness just being friendly to people, offering them something you care about and having them be friendly back. Look at village cafés that are always full of people. A good mood and care brings one way further than pushing every client to pay those 3 bucks extra.

Be decent, be friendly. Be happy.

Business Dictionary

Some things i’ve come around over the years that i had to look up.

CapEx – capital expenditure > money spent at once as an investment
OpEx – operational expenditure > money spent on a recurring basis

USP – unique selling point > Something you can offer to customers that noone else does.

B2B – Selling to other businesses
B2C – Selling to consumers

ROAS – Return on ad spent > How much do you earn for every dollar spent on ads.
ROI – Return on investment > How much do you earn back for every dollar spent as an investment.

KPI – key performance incators > Statistics that show how good your business is doing.

R&D – Research & Development > Area of your business dealing with creating and improving products.

A/B Testing – Testing multiple version of a page to see which one gains more conversions
CTR – Click through rate > How many people click through to another page or on your ad.

PPC – Pay per click > Paid ads
SEO – Search engine optimization > Organic traffic through google
CRO – Conversion rate optimization > Trying to get more conversions as a percentage of visitors.

COR – Cost of revenue > the cost of producing and delivering a product to customers, excluding indirect costs such as marketing and R&D. The part of expenses that doubles if the number of sales doubles.

Marketing a B2B company

These are some things to try when it comes to b2b marketing.


Referrals are everything in B2B. The largest amount of jobs comes from previous employers or friends. This is even more true for government jobs.

Social media

Make social media accounts, linkedin, facebook, twitter, instagram. Respond to posts of other companies and post your own content that may help other people so your posts get shown to more people that will recognize your name and may convert.


Build tutorials

Build a blog with tutorials, this helps greatly with SEO but also just people knowing your company. Digitalocean does an awesome job with this.


Well. the above. Find long-tail keywords without too much competition and start with those.


paid ads suck but might be worth a try. Think google’s banner ads. Search engine ads, facebook/insta. Or maybe one of your niche’s forums. Retargeting also makes this quite a bit more useful.

Sponsor popular projects.

If your niche has projects that are used by a lot of people that might also be interested in your product, pay for their needs and offer them your infrastructure. Referrals from a project owner or banners on popular projects are a great way to gain more clients.

Linkedin marketing

Linkedin is still he home of businesses, post messages, connect with others and learn about the market and demands.

Build a mailing list

Email is dead… But still useful. As long as you deliver emails that people actually read they can be a great way to keep an audience in on your company. Make these emails entertaining and full of information. Keep in mind most people don’t care about your company, they care about their own.

Already have forgotten it by the time they get to the next mail in their mailbox.

For the love of god please don’t just send e-mails whenever you do an acquisition or seeding round. Yes bigger companies might gain slightly more trust if you have the funds but will already have forgotten it by the time they get to the next mail in their mailbox. Get someone’s interest and make them memorable.

Advertise on more niche platforms.

Be active on platforms like discord if your target demographic is mainly younger audiences or make sure you are active on forums in your area. Think of hosting forums, electrical support, etc etc. These people have demands in your area and helping them increases your brand awareness and trust by a lot. Even when someones comes across your post x years in the future.

Do you have more tips that worked for your company? Please suggest them in the comments so i can improve this guide.

Sales: Some tactics

These are some sales & CRO tactics and tips i’ve seen used on me for the last couple of years.

Decoy products

Add a product that looks like a bad deal, so a slightly more expensive product looks like a great deal.

Not many buyers? Up the price!

Again more of a marketing thing.
It might be counter-intuitive, but before you try to lower the prices, try to put it up first. More expensive products are generally rated better and you can deliver a better product. And if your product is priced in the middle of your other products you will probably not reach the cheapest customers and not the well-paying ones.

Tip: never give people your biggest product

Unless they actually actively ask for the best of the best and budget does not matter, please don’t. It looks like you just want to sell sell sell and not actually listen to the customers. Listen to your customers and sell them something that fits them. Long-term happy customers are worth way more than someone that will be turned off because you quoted too much.

Sometimes less is more

Perceived value is important. If you are selling a lot of awesome stuff very cheaply, and you don’t want to up the price for whatever reason, then try to take away a bigger but not vital part of your offer. For example only offer a single PDU instead of redundant ones. This will justify the lower price to your client and they can think its not really needed anyway. You can even decide to still give them that feature afterwards as a extra means of making the customers happier and thus more likely to stay with you in the long term.

The choice paradox: too little or too much

Your mind tricks you into thinking that you like choice. But studies have shown that you will often buy more if you have less choice because there is less chance of buyer’s remorse.

“Forgetting” part of the price

This happens too often and it’s just a shitty business practice but it does work. If someone is really shopping for a medium-sized amount of money but with little margin, you often have people give you a really good deal, and then after you are all hyped up about it add 10-15% because of “power costs” or the like.

Grow a following

This works really well in lower-value B2C areas like game hostings. Some companies have managed to make almost a cult that will advertise and protect the brand because they feel like they associate with it. This kind of advertising is the best you can get because its free and you reach people that are in similar groups.

Use the same language as your buyer

If your customer is younger and talking in a “Chill” kind of way. Also talk like that on the same level. If you are talking to someone in suit that prefers to keep everything in order, mirror that. If people can associate themselves with your company that is a very easy way to get more sales. A lot of companies lose out on younger clients because they try to be overly-professional or (funny, but not as trustable) overly-cool.

TIP: Push, but don’t push too hard

You want your client to feel like they have made the right choice. If you push too hard they will start to doubt and further pushing will only push them away. Show them what you’ve got and “guide” them down the right path for them with good questions.

Limited-time deals

There are two types of this:

1: have deals that are only valid for a limited amount of time. Eg summer/winter/whatever.

2: When doing sales, ask someone to repond within x days or the end of the month or else the price wll be higher. I personally hate this tactic but it does help with pushing people over the edge.

Sell features, not specs

People don’t care about how many watts your generator can do. They care about reliability, price, and time. Look at apple’s marketing for some great examples “10000 songs in your pocket” instead of “20GB of storage”.

Reach out before a sales meeting

Connect on linkedin, send them a friendly e-mail. As always: don’t overdo. If your client is warmed up and has some interest in what you are selling then your sales meeting will go way smoother. And worst-case scenario you have a new linkedin contact that might become a buyer in the future.

Say something positive before upselling

Being friendly is ofcourse always good. But saying something that makes the client feel good about themselves is even better.
An example would be with driver’s lessons. Companies will always let you drive yourself for the last part of the introduction lesson. And after that the sales rep will ask you “Has she let you drive & steer alone already?” giving you the feeling that that is something very positive about you. And then go to the high(er) pricing. Another example of this is complimenting a customer’s website of growth.

Show knowledge about the customer’s market

For example, call out spikes in popularity or other special events related to the customer and also (if you can) talk customer’s competitors that are using you. This gives the customer more trust in your business and calling out competitors will give them more of a feeling that they are missing out on something.

If you have no clue about the customers market and have noone on your team that does, don’t talk bullshit. I have never left a sales meeting faster than when the salesperson was talking about their own product in a way that showed they had no clue what i was looking for.

Be an account manager, not a salesman.

People hate sales, people hate marketeers. But if the person pitching to you is an account manager (or just a salesman called a account manager) then it will feel like they care more about individual customers, and thus also you.

Mirror the customer’s values and platforms

For game clients, use Discord. If the business uses zoom use zoom. If the client feels more at home they will be happier to talk to you.

It also really helps to mirror things the client says that also apply to your company. E.g. always being open to improvement or laying high importance on customer support and uptime.

Referrals are gold

Referrals go far in every b2b market. Don’t actively ask for referrals of new clients, but ask your more social clients if they know someone who might be interested or ask your bigger companies if they can fill in a short survey on why they recommend your company. For bigger companies donating x$ for every response often works better than offering gift cards.

Keep up a mailing list

Maybe your client does not want to buy from you now for whatever reason. Add them to your mailing list and keep them updated with an e-mail every x months. You should really not spam this list or instantly start sending emails. A good mailing list is a very valuable asset and will give you many pre-warmed leads later on. Even ex-clients are a great source of referrals and new orders as they already know and trust your company.

Personalisation is key

It’s shown again and again that even just adding someone’s first name in your email subject will increase the clickthrough rate by a lot.

A different kind of personalisation also helps: Sign your emails with a real name. Don’t use “x’s marketing team” but “Luc – VP of x” (or just leave the title out altogether.

Human contacts, with automated possibilities.

Customers want to feel valued and safe. Show the customer who will be helping them while they are a client. But also show that things can be done quickly without waiting for slow humans.

B2B clients care about reliability more than everything

Fintech is an extreme example of this. But all b2b clients generally put more importance in reliability of your platform than price or value. Their business depends on you so show them that you will not let them down.

With this: Call out 1-2 cases where you failed reliability and how you solved this. I can trust a salesperson that can recount all downtime from their head a lot more than one that says they never have downtime (given that it’s handled well and not too often). Because it just can’t be true.

Find your main selling point

Find out what kind of things your clients are often looking for when they choose for your business or maybe what they are looking for when they decide not to go for your business. Companies that have a unique product often do great, but sometimes you can also run a company purely on being cheaper or higher quality than others.

Talk about the things your customer wants to know.

Be quick

Contacting your client within minutes of the lead being generated increases the likelihood of closing a sale by a lot, but make sure to leave enough time during which the client can call. Don’t call a big business during the weekend or outside of business hours. If you wait for more than a week the lead is almost guaranteed to be lost. (But you can always say that you were sick, looking at a specific company here)

Call from a trusted number

Make sure that you use a number local to the customer that they are likely to pick up. Try to register in SMART registers that will show your business name when calling someone on a smartphone.

If you know that your customer is using a specific chat platform internally then it is a great idea to use that. The customer will feel more at home and focussed on the talk and not on other distractions.

Not the right client?

If your client shows that your product is not a good fit, ask them for feedback on what to improve for “future clients”. This will help you improve your product and have a better product for new clients, maybe show that you can offer what your client is looking for or even find a broader market with demand that you can jump into.

The DDoS Problem pt. 1: Legal

As someone in the gaming market, I experience DDoS attacks on a regular basis. While there are numerous “solutions” this problem is still far from solved.

Legal problems

A person that was attacking us on a almost daily basis was really getting on our nerves. We had many clients complain and also lost out on a good amount of profit due to our services being inaccessible for even short periods of time.

Luckily for us, most of these criminals are often young and not the smartest people around. He regularly posted photos of our website being offline in the discord group where he was selling his services and also leaked out his personal information online at numerous places due to previous endeavors. I decided it was enough and filed a police report. Our government is modern enough to have a page to say cybercrime and DDoS are illegal, but have no official way of reporting them without talking to someone who has no idea what you are talking about.

*cue long wait*

After multiple months, I finally got a call back from the central police station asking for more information which I happily submitted.

Then I got another call, “Since we are highly understaffed we have dropped your report, please let us know if you need anything else”.

Is this what i pay my taxes for (spoiler: no)?

I have lost hundreds if not in the thousand of euros due to these attacks, but they don’t think that’s enough value to start a valid case even though the attacker gave in to them that he did indeed attack us and numerous others.

The person on the phone offered to go and talk to the attacker (for which we had a phone number and address) which i reluctantly agreed to.

Fun fact: A lot of cyber criminals get offered a job at the government after they get caught.

Fun fact: A lot of cyber criminals get offered a job at the government after they get caught. One might say executing ddos attacks is a easier way to get a well-paying job than just applying. To be completely fair i wasn’t expecting much of our legal system. We had the minesearch case a while back where a very active booting site was taken down and the owners arrested after their personal information was online for years. The owners of this site were allowed out of police custody within days of being caught.

Luckily most of the ddos activities from that person seemed to have stopped there, but he was just one of many and the fight is far from over.

Tldr; Our legal system is not built to tackle cybercrime. Cybercrime is an ongoing issue that will only grow with time and will be immensely disruptive to future businesses and governments in any sector and will definitely need solving on a technical and legal level.

Please share your thoughts below. I love hearing other people’s experiences with this problem. Please note that this post is talking about my experience in the Netherlands. I have heard that a small amount of other countries are doing a better job at keeping up with the modern world.