There is a language L such that L is not recursive (L is undecidable), yet L and its complement are both recursively enumerable. 因为英文水平太差，所以急需援助下面这道英文的题目，不知道能不能给我翻译一下，实在是理解不了： 题目：Consider the following statements: I.
Only recently, in 2015, did mathematicians prove that in general the spectral gap question is undecidable.
直到最近的 2015 年，数学家才证明谱隙问题一般是不可判定的。
Veritasium真理元素
Although they are powerful, every Turing-complete system comes with a catch, its own analog of the halting problem, some undecidable property of the system.