foo.c: In function 'main':
foo.c:11:17: warning: implicit declaration of function 'gcd' [-Wimplicit-function-declaration]
   11 |             if (gcd(i, j) == 1) {
      |                 ^~~
/nix/store/j2gmfdd29cp3rcvghmn1a5kgcnmf8myp-binutils-2.40/bin/ld: /tmp/cciMWIwA.o: in function `main':
foo.c:(.text.startup+0x4b): undefined reference to `gcd'
collect2: error: ld returned 1 exit status

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