<p>How can you express X of Y are true, in boolean logic?  a rule like 2 of the following must be true (A, B, C, D, E, F)
is it a form of multiplcation or set operations?<br>
the end result is all the permutations like AB OR AC OR AD, if you said 3 of following it is like ABC, ABD, ABE, etc.. so it is like (A,B,C)^2?</p>

<p>thanks!</p>

You've got the idea there.  To express "k of n holds" you're going to need to enumerate all cases for which k holds.  So, if we have variables A B C D E, and you want 3 of 5, you'll need
```
```
(A  &  B &  C & ~D & ~E) |
(A  &  B & ~C &  D & ~E) |
(A  &  B & ~C & ~D &  E) | ...
(~A & ~B &  C &  D &  E)
```
```
where & is "and", | is "or" and ~ is "not".