Predicted by the Dirac equation.
We've likely known since forever that photons are created: just turn on a light and see gazillion of them come out!
Photon creation is easy because photons are massless, so there is not minimum energy to create them.
The creation of other particles is much rarer however, and took longer to be discovered, one notable milestone being the discovery of the positron.
In the case of the electron, we need to start with at least enough energy for the mass of the electron positron pair. This requires a photon with wavelength in the picometer range, which is not common in the thermal radiation of daily life.
This is the order in which a binary search tree should be traversed for ordered output, i.e.:
This ordering makes sense for binary trees and not k-ary trees in general because if there are more than two nodes it is not clear what the top node should go in the middle of.
This is unlike pre-order depth-first search and post-order depth-first search which generalize obviously to general trees.
The Taylor series expansion is the most direct definition of the expontial as it obviously satisfies the exponential function differential equation:
Using de novo DNA synthesis to synthesize a genes to later insert somewhere.
Note that this is a specific application of de novo DNA synthesis, e.g. polymerase chain reaction primers is another major application that does not imply creating genes.
LeetCode by Ciro Santilli 37 Updated 2025-07-16
Their system is quite good actually. Not as good as a GitHub repo with all the tests made explicit. But still pretty good.
Platform as a service by Ciro Santilli 37 Updated 2025-07-16
Highly managed, you don't even see the Docker images, only some higher level JSON configuration file.
These setups are really convenient and cheap, and form a decent way to try out a new website with simple requirements.
Sometimes you are really certain that something is a required substep for another thing that is coming right afterwards.
When things are this concrete, fine, just do the substep.
But you have to always beware of cases where "I'm sure this will be needed at some unspecified point in the future", because such points tends to never happen.
YAGNI is so fundamental, there are several closely related concepts to it:
Figure 1.
xkcd 2730: Code Lifespan
. Source.
Once upon a time, when Ciro Santilli had a job, he had a programming problem.
A senior developer came over, and rather than trying to run and modify the code like an idiot, which is what Ciro Santilli usually does (see also experimentalism remarks at Section "Ciro Santilli's bad old event memory"), he just stared at the code for about 10 minutes.
We knew that the problem was likely in a particular function, but it was really hard to see why things were going wrong.
After the 10 minutes of examining every line in minute detail, he said:
I think this function call has such or such weird edge case
and truly, that was the cause.
CSS flex by Ciro Santilli 37 Updated 2025-07-16
  • css/flex.html: illustrates basic flex usage, including:
  • flex-grow: if there's space left, this determines how much extra space will be given to each.
  • flex-basis: the size the items want to be. But if there isnt' enough space, this can be cut up.
    Note that the minimal space required by children of the flex children cannot be necessarily cut up, and might lead things to overflow out of the container.
  • flex-shrink: if there's space missing, this determines how much extra space will be removed from each flex-basis
Other examples include:
That example calculates and displays the final widths via JavaScript, making it easier to understand the calculations being done.

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