What is a concise easy to read way of testing to see if two numbers out of three are equal?

Question

Basically, if I have a function like so:

function foo (int a, int b, int c) {
    return true if two out of the three variables are true otherwise false
}

Is there a simple and concise way to find out if there are n numbers are equal out of a set? What about only three items? Is there a mathematical operation that I can take advantage of? I know that I can do an iterative approach to solve, I'm just curious if there are other ways to solve that are clearer.

Here is a break down of conditions because I'm having a hard time expressing the problem:

if no numbers are equal, return false
if two numbers out of three are equal, return true
if all three numbers are equal, return false

Answer 1

One method would be to add the parameters to a set and then see if the length of that set is equal to 2 (or less than 3 if you it to return true if they are all equal as well). For example, in Python:

def foo(a, b, c):
    return len(set((a, b, c))) == 2

Answer 2

I don't think you're going to get any more efficient or concise than the manual way:

if a == b 
   return b != c 
else
   return b == c || a == c

Or else this:

return ((a == b) || (a==c) || (b==c)) && ((a!=b) || (a!=c) || (b!=c))

If a, b, and c are boolean only (0 or 1) values, then you can just do this:

return a+b+c == 1 || a+b+c == 2 // Either two are false, or two are true