Is implicit function declaration legal in C89?

Question

Consider this C program:

int main()
{
    puts(\"Hello world!\");
    return 0;
}

This compiles and runs fine and as far as I understand, i

Answer 1

Is implicit function declaration legal in C89?

Yes. From section 3.3.2.2:

If the expression that precedes the parenthesized argument list in a function call consists solely of an identifier, and if no declaration is visible for this identifier, the identifier is implicitly declared exactly as if, in the innermost block containing the function call, the declaration

    extern int  identifier();

appeared.