# Jorge Fernández

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bio website location Mexico City age member for 2 years, 6 months seen 19 hours ago profile views 1,980

Hello, I am a freshman at The National Autonomous University of Mexico (UNAM).

My interests are contest problems,elementary number theory, combinatorics, graph theory, linear algebra, group theory, abstract algebra and I have been meaning to learn category theory and matroids.

 20h comment Bounds on the numbe of groups of degree n Oh, I had never seen the power of the gold badge tag been laid down like that, it was pretty hardcore. 20h comment Group theory, the squares of G you already proved it is normal. When $N$ is normal $gNhN=ghN$ 20h comment Set of common representatives and pigeonhole principle in one problem Oh I see. thank you very much. 20h comment if $A$ and $B$ are subnormal, then $A\cap B$ is subnormal Did I make a mistake? 22h comment an example for an arbitrary graph $G$ with even vertices which $\forall S \in V(G) , |N(S)|\geq |S|$ but there is no complete matching . yeah, odd cycles do the trick, but he wants a connected one. 1d comment What is the largest $k$ such that $\frac { k(abc) }{ a+b+c } \le \left( a+b \right) ^{ 2 }+\left( a+b+4c \right) ^{ 2 }$? Are the values poditive real numbers, otherwise we can take one of teh values as zero and the left becomes zero. 1d comment What is the largest $k$ such that $\frac { k(abc) }{ a+b+c } \le \left( a+b \right) ^{ 2 }+\left( a+b+4c \right) ^{ 2 }$? Also, what kind of variables do we have? 1d comment What is the largest $k$ such that $\frac { k(abc) }{ a+b+c } \le \left( a+b \right) ^{ 2 }+\left( a+b+4c \right) ^{ 2 }$? is this really level 5? 1d comment Set with distinct subset sums Yeah, but the repeated elements are not in the generating set, so it doesn't matter. 1d comment Triangle-free graph with 5 vertices You can also apply turan's theorem and it follows directly. 1d comment Triangle-free graph with 5 vertices Well, you can simply apply turan's theorem and you get the triangle free graph on $n$ vertices with most edges is always the complete bipartite graph in which both parts have as close a number of vertices as possible. 1d comment $x^2-y^2=2s$, s cannot be an odd integer Oh, this solution is much better than mine. +1 1d comment Triangle-free graph with 5 vertices with $5$ vertices. If there is no restiction on the number of vertices you can find a bipartite graph with as many edges as desired. 1d comment Triangle-free graph with 5 vertices Oh, we thought of the same thing, they say poor minds think alike. 1d comment Number of ways to arrange items $f_k(n)$ are the same as the stirling numbers of the first kind 1d comment Minimize total cost of one kilometer Something is wrong, the cost per hour should always be over $100$. are you sure the cost per hour is $25$ when the speed is $25$? 1d comment How to solve this kind of problem? I solved it using integers, I think it becomes harder if we can only use naturals. 1d comment Check if Sequence is Graphic: 8, 8, 7, 7, 6, 6, 4, 3, 2, 1, 1, 1 I mean, you should count the degrees in the graph to make sure, but I can't find more conclusive evidence it is graphic 1d comment Check if Sequence is Graphic: 8, 8, 7, 7, 6, 6, 4, 3, 2, 1, 1, 1 Well, I counted the degrees in the graph in the solution and it is correct, are you sure you copied the sequence correctly? 1d comment How to solve this kind of problem? The number in the bottom right corner has to be $1,-1,11$ or $-11$