Four pairs of lords and ladies all went to a royal ball. Each lord was wearing one color (yellow, red, blue, or green) and each lady was also wearing one of these colors. No couple was wearing the same color, so it was hard to tell who was married to who.
Using the clues, can you determine which lord is with which lady?
1. The Green Lord is with the Red Lady, if and only if the Yellow Lord is with the Blue Lady.
2. The Yellow Lord is with the Red Lady if and only if the Green Lord is with the Yellow Lady
3. The Red Lord is with the Blue Lady, if and only if the Green Lord is with the Red Lady.
(In reply to A far easier solution
by Federico Kereki)
Lest someone *does* believe in my "quick-sure-fire-solve-everything" method, here's a nicer solution:
(1) and (3) imply that if the Green Lord was with the Red Lady, the Blue Lady would have to be with two different Lords, so the Green Lord isn't with the Red Lady. Therefore, the Blue Lady isn't with either the Yellow or Red Lords: she must be with the Green Lord.
From the previous and (2), the Yellow Lord isn't with the Red Lady, and from (1), he isn't with the Blue Lady either: he must be with the Green Lady.
Finally, the Red Lord is left only the Yellow Lady, and the Blue Lord can only be with the Red Lady.