Multiple declaration for 'oldHotkey' - C (СИ)

#include < dos.h >
#include < conio.h >
#include < stdio.h >
void interrupt far (*oldKeyHandler)(...);//Blocked f6
void interrupt far (*oldHotkey)(...);//fiLter shift+alt+f
 
unsigned char  SCAN_F6= 64;
unsigned char  SCAN_Shift= 16;
unsigned char  SCAN_ALT= 12;
unsigned char  SCAN_f= 102;
int keycount=1;//count shift+alt+f
/////////////////////////////////////////////////////////////////////////////////
 
void interrupt far keyHandler(...) {
char key = inport(0x60);
 
//blocked f6
if ((key==SCAN_F6) &&  (keycount%2)==0)
{
char ctr = inport(0x61);
outport(0x61, ctr | 0x80);
outport(0x61, ctr);
outport(0x20, 0x20);
printf("key F6 is blocked.");
textattr(0x0f);
} else oldKeyHandler();
}
//////////////////////////////////////////////////////////////////////
 
void interrupt far oldHotkey(...) 
{
char key = inport(0x60);
if (key==SCAN_Shift) &&(key==SCAN_ALT)&& (key==SCAN_f){
keycount=keycount+1;
}
}
 
/////////////////////////////////////////////////////////////////////////////
int main() {
 
clrscr();
textattr(0x0a);
cprintf(" ");
cprintf(" Laboratorna rabota #2");
cprintf(" ");
cprintf(" Control keyboard");
cprintf(" ");
 
textattr(0x0c);
cprintf("\n\n\r"hot" combination: "); textattr(0x0a);
cprintf(" Shift+Alt+f\n\r"); 
textattr(0x0b);

oldKeyHandler = getvect(0x09);
setvect(0x09, keyHandler);
oldHotkey = getvect(0x09);
setvect(0x09, oldHotkey);
char c;
 
do {
c = getch();
if (c==0)
 {printf("*");
c=getch();
}
 
printf("\t%c : %u\n", c, (unsigned int)c);
} 
 
while(c!=27);
return 0;
}