I need some help with a simple problem involving the basic logical operators: AND, OR, and NOT, along with the relational operator EQUAL TO, and truth values TRUE and FALSE.

Let's assume that we have a function tD() that tests whether 3 integers are all different. So, tD( 1, 2, 2 ) will return FALSE, and tD( 6, 6, 6 ) will return TRUE.

Now, my problem is to define a function the uses the above to determine whether or not 4 integers are equal. Let's call it

bool fE( a, b, c, d )

defined completely in terms of

bool tD( a, b, c) 

and the aforementioned operators.

you can write in any code you prefer.