已知集合\(S=\left\{a_1,a_2,a_3,\cdots,a_n\right\}\)(\(n\geqslant 3\)),集合\(T\subseteq\left\{\left(x,y\right)\left|x\in S,y\in S,x\neq y\right.\right\}\)且满足\(\forall a_i,a_j\in S\)(\(i,j=1,2,3,\cdots,n,i\neq j\)),\(\left(a_i,a_j\right)\in T\)与\(\left(a_j,a_i\right)\in T\)恰有一个成立.对于\(T\)定义\[d_T(a,b)=\begin{cases}1,(a,b)\in T,\\0,(b,a)\in T,\end{cases}\]以及\[l_T\left(a_i\right)=d_T\left(a_i,a_1\right)+d_T\left(a_i,a_2\right)+\cdots+d_T\left(a_i,a_{i-1}\right)+d_T\left(a_i,a_{i+1}\right)+\cdots+d_T\left(a_i,a_n\right),i=1,2,3,\cdots,n.\]
(1)若\(n=4\),\(\left(a_1,a_2\right)\),\(\left(a_3,a_2\right)\),\(\left(a_2,a_4\right)\in T\),求\(l_T\left(a_2\right)\)的值及\(l_T\left(a_4\right)\)的最大值;
(2)从\(l_T\left(a_1\right)\),\(l_T\left(a_2\right)\),\(\cdots\),\(l_T\left(a_n\right)\)中任意删去两个数,记剩下的\(n-2\)个数的和为\(M\).求证:\[M\geqslant \dfrac 12n(n-5)+3.\]
(3)对于满足\(l_T\left(a_i\right)<n-1\)(\(i=1,2,3,\cdots,n\))的每一个集合\(T\),集合\(S\)中是否都存在三个不同的元素\(e\),\(f\),\(g\),使得\[d_T\left(e,f\right)+d_T\left(f,g\right)+d_T\left(g,e\right)=3\]恒成立,并说明理由. 继续阅读 →