Theorem numbering in LaTeX

Question

I have a problem with theorem numbering in LaTeX. I can make it number by subsection, e.g

Theorem 1.2.1

for the first theorem in

Answer 1

In a slightly less hacky way, you may create a fake counter that is reset with subsection, and redefine its \the to your liking:

\newcounter{fakecnt}[subsection]
\def\thefakecnt{\arabic{subsection}}
\newtheorem{thm}{Theorem}[fakecnt]