When I am trying to code in the math mode, the compiling process is terminated under any environment. How may I solve it?

Let $\mathbf{A}$ be the set of $n \in \mathbb{N}$ that 
  • 5
    As always on this site please make this into a full minimal example. Document class and preamble is missing. Might also be a good idea to cite the actual error message. Given what you have here my guess is that you have forgotten to load amssymb or any similar package that provides \mathbb
    – daleif
    Aug 31, 2019 at 17:08
  • 2
    Load amsfonts?!
    – Sigur
    Aug 31, 2019 at 17:14
  • 1
    Please check the exact error message. Does it maybe say "! Undefined control sequence." rather than "Undefined sequence error"?
    – Mico
    Sep 1, 2019 at 4:24
  • Thank you all for your kind assistance, it turned out that the problem is incurred simply because I didn't use the packages, I'll also try harder to state more clearly the next time! Sep 5, 2019 at 1:07

1 Answer 1


As others have already commented, you almost certainly failed to load the amssymb package in the preamble of your document. (Aside: The amssymb package loads the amsfonts package automatically.) For sure, the following example, which loads the amssymb package, compiles without any problems.

\usepackage{amssymb} % <-- important
Let $\mathbf{A}$ be the set of $n\in\mathbb{N}$ such that  \dots

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