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Questions about the branch of algebra that deals with groups.

10 votes

1 rectangle <= 4 squares

The upper bound is <3.95. I hope the code below will show correctly... It proves that assuming a sum >=3.95 in the central AxB rectangle of the grid ({-B,-B+A,-2A,-A,0,A,2A,B-A,B}+{0,A}) x ({-2B,-B- …
Yaakov Baruch's user avatar
4 votes

1 rectangle <= 4 squares

Here is a summary for the $\mathbb{R}^2$ situation. Upper limit: no improvement over the 3.8 known on $\mathbb{Z}^2$. To create specific examples I modified the $\mathbb{Z}^2$ ones by uniformely spr …
3 votes

1 rectangle <= 4 squares

There is a new upper bound of 254/67 (= 3.79104477...). Define 6 sets of cardinality 4: X1={-B+A, 0, A, B} Y1={0, A, B-A, B} X2={-B, -B+3A, B-2A, B+A} Y2={-2B+A, -A, B+A, 3B-A} X3={-6B+2A, -2B-2A, …
42 votes
8 answers
4k views

1 rectangle <= 4 squares

Almost 25 years ago a professor at Indiana U showed me the following problem: given a map $\mathbb{Z}^2\rightarrow\mathbb{R}$ such that the sum inside every square (parallel to the axes) is $\leq1$ i …