Rationale of static declaration followed by non-static declaration allowed but not vice versa

Question

This code will compile and is well defined under current C standards:

static int foo(int);
extern int foo(int);

The standard specifies that

Answer 1

I think the idea of this confusing specification is that an extern declaration can be used inside a function to refer to a global function or object, e.g to disambiguate it from another identifier with the same name

static double a; // a declaration and definition

void func(void) {
  unsigned a;
  .....
  if (something) {
     extern double a; // refers to the file scope object

  }
}

Whereas if you use static you declare something new:

extern double a;  // just a declaration, not a definition
                  // may reside elsewhere
void func(void) {
  unsigned a;
  .....
  if (something) {
     static double a; // declares and defines a new object

  }
}