/in/isSibling.c: In function 'isSibling':
/in/isSibling.c:13:11: warning: implicit declaration of function 'strlwr'; did you mean 'strlen'? [-Wimplicit-function-declaration]
     word1=strlwr(word11);
           ^~~~~~
           strlen
/in/isSibling.c:13:10: warning: assignment makes pointer from integer without a cast [-Wint-conversion]
     word1=strlwr(word11);
          ^
/in/isSibling.c:14:10: warning: assignment makes pointer from integer without a cast [-Wint-conversion]
     word2=strlwr(word22);
          ^
/tmp/ccSdVGns.o: In function `isSibling':
isSibling.c:(.text+0x71): undefined reference to `strlwr'
isSibling.c:(.text+0x88): undefined reference to `strlwr'
collect2: error: ld returned 1 exit status