/tmp/ex4-cd5a56.o: In function `main':
/in/ex4.c:7: multiple definition of `main'
/tmp/main-ea3089.o:/in/src/main.c:10: first defined here
/tmp/main-ea3089.o: In function `main':
/in/src/main.c:19: undefined reference to `ex4'
clang: error: linker command failed with exit code 1 (use -v to see invocation)