messy.h:1:9: warning: #pragma once in main file
    1 | #pragma once
      |         ^~~~
messy_c.h:1:9: warning: #pragma once in main file
    1 | #pragma once
      |         ^~~~
/usr/bin/ld: /tmp/ccgB75hR.o: in function `main':
grader.cpp:(.text.startup+0x16f): undefined reference to `restore_permutation(int, int, int)'
collect2: error: ld returned 1 exit status