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visits member for 2 years, 9 months
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Oct
26
asked Finite models for Systems of Incidence and Parallelism Axioms?
Oct
25
comment Clarification on labelled graphs?
@bof Oh, yes. A path must take all the vertices. I confused $P_3$ with arbitrary simple graphs on $3$ vertices. I know it now.
Oct
25
asked Clarification on labelled graphs?
Oct
25
asked How to show that $at^2+bt+c$ can be written as $\displaystyle \begin{equation} a \left( t+\frac{b}{2a}\right) ^2-\frac{1}{4a}(b^2-4ac)\end{equation}$?
Oct
25
comment Showing the equality of two rook polynomials.
Oh, yes. I just saw it now. Thanks.
Oct
25
accepted Is there something that studies equivalent forms of writing and expression?
Oct
24
answered Show that if $a,k\in \mathbb{Z}$ with $0\leq k \leq a$, then $\binom ak=\frac{a!}{k!(a-k)!}=\binom {a}{a-k}$.
Oct
24
comment Showing the equality of two rook polynomials.
"If there is a rook on $S$, there cannot be any rook in the entire row or column containing $S$" - Why? I don't get it. Take for example the following chessboard: $$\begin{matrix} {\bullet }&{\underline{\bullet}}&{\bullet}&{\bullet}\\ {\underline{\bullet}}&{\star }&{\underline{\bullet}}&{\underline{\bullet}}\\ {\bullet}&{\underline{\bullet}}&{\bullet}&{\bullet}\\ {\bullet}&{\underline{\bullet}}&{\bullet}&{\bullet} \end{matrix}$$ It has a rook on $(2,2)$, it could also have rooks in all the remaining squares, no?
Oct
21
revised Showing the equality of two rook polynomials.
edited tags
Oct
21
asked Showing the equality of two rook polynomials.
Oct
19
awarded  Nice Question
Oct
17
comment Show that $\mathbb{N}=\{ 0\} \sqcup S(n)$ and also that that union is disjoint?
@GregMartin I've corrected it.
Oct
17
revised Show that $\mathbb{N}=\{ 0\} \sqcup S(n)$ and also that that union is disjoint?
added 27 characters in body
Oct
17
asked Show that $\mathbb{N}=\{ 0\} \sqcup S(n)$ and also that that union is disjoint?
Oct
15
accepted Is $\frac{4n^2+4n+1}{8}$ an integer for any $n\in \mathbb{N}$?
Oct
14
asked Is $\frac{4n^2+4n+1}{8}$ an integer for any $n\in \mathbb{N}$?
Oct
13
asked How to solve $\frac{15!}{(x-1)!(16-x)!}=\frac{15!}{(2x+1)!(14-2x)!}$ for $x$?
Oct
12
asked How to verify this recursion and how does the assertion follows immediately?
Oct
11
awarded  Disciplined
Oct
7
awarded  Good Question