DeMorgan's Theorems state

!(A || B) == (!A && !B)

!(A && B) == (!A || !B)

Where A and B represent either a 0 or 1.

Assume the function f() is defined as

int f()
{
  return(1 && (30 % 10 >= 0) && (30 % 10 <= 3));
}

Applying DeMorgan's Theorem to the function f() means all these conditional statements will return true or 1 in the C programming language.

!f()  == !(1 && (30 % 10 >= 0) && (30 % 10 <= 3))   
!!f() == (!1 && !(30 % 10 >= 0) && !(30 % 10 <= 3)) 
f()   == 0 || (30 % 10 < 0) || (30 % 10 > 3)