theorem Th36: :: DIFF_2:36

for x0, x1, x2, x3, k being Real
for f being Function of REAL,REAL st ( for x being Real holds f . x = k / x ) & x0 <> 0 & x1 <> 0 & x2 <> 0 & x3 <> 0 & x0,x1,x2,x3 are_mutually_distinct holds
[!f,x0,x1,x2,x3!] = - (k / (((x0 * x1) * x2) * x3))