I've been playing "binary sudoku". You have a 2nx2n grid, with some 0s and 1s and you have to fill it in according to some rules:

* each row and column has equal number of 0s and 1s

* no row or column has a run of three 0s or 1s

* no pair of rows is the same

* no pair of columns is the same

conjecture: there must be a pair of rows (or columns) that are "inverse" i.e. a pair of strings s t where s[i]=/=t[i] for all i.

I can see a boring case analysis proof but is there an "at a glance" proof?

I'm sure many of you have seen this, it's a couple of years old - there's a sort of lattice of quadrilaterals (a square is a rectangle is a parallelogram etc) but it's a bit ugly if you stick to standard named ones. Here a "kitoid" is introduced to make a really beautiful diagram

https://www.hambrecht.ch/blog/2017/7/26/the-quest-for-the-lost-quadrilateral

But it got me thinking, is there any well defined sense in which these categories are exhaustive (for convex quads)? And if so how many are there for n-gons

So for example \(C_7^{1,2}\) is the graph on {0,1,2,3,4,5,6} with an edge uv if and only if u-v is in {1,2,-1,-2} mod 7. The sequence is like this

\(C_3^0,C_4^2,C_5^1,C_6^{1,3},C_7^{1,2},C_8^{1,2,4},C_9^{1,2,3}\ldots\)

See the graphs labelled 3...9 (ignore the other doodles)

"In the new commission the areas of education and research are [...] subsumed under the "innovation and youth" title. This emphasizes economic exploitability (i.e. "innovation") over its foundation, which is education and research, and it reduces “education” to “youth” while being essential to all ages...

With this open letter we demand that the EU commission revises the title for commissioner Gabriel to “Education, Research, Innovation and Youth”"

@christianp

I like the three color addition! Is this a common property of projective planes (maybe it's trivial?...I'm not used to thinking about the points as repeated like this! 🙂 ) or one of the named adjectives (Desarguesian, etc.)?

I realise now that the way I have been saying this fact is very ambiguous (I can make it make sense with tone of voice and hand gestures).

I mean to say there is exactly one number that is the successor of a square and whose successor is a cube, or to put it another way, there is exactly one solution to y³-x²=2 with x,y integers.

3/n

Mathematician, computer scientist, bassist, knitter?

Joined Jan 2018