<locale> imported indirectly if
<algorithm> is included?
There is no import (before C++20 and
modules) in C++11, just
includes. Read n3337 (or some newer C++ standard), the documentation of your compiler (e.g. GCC) and preprocessor (e.g. GNU cpp).
If you use GCC, compile your C++ code
g++ -Wall -Wextra -g -H -c mathworker.cc and you will see what files are
On some implementations it could happen that
<locale> gets included.
But if you care about portability to other C++ compilers (like Clang, or a newer version of GCC) you should code explicitly the
#includes documented in e.g. this C++ reference.