Alice came across a lion and a unicorn in a forest of forgetfulness. Those two are strange beings.
Lion lies every Monday, Tuesday and Wednesday and the other days in week he speaks the truth.
Unicorn lies on Thursdays, Fridays and Saturdays, however the other days in week he speaks the
truth.
Lion: Yesterday I was lying.
Unicorn: So was I.
Which day did they say that?

As there is no day when both of the beings would be lying, at least one of them must
have spoken the truth. They both speak the truth only on Sunday. However, the Lion
would then be lying in his statement, so it couldn’t be said on Sunday. So exactly one of
them lied.
If the Unicorn was honest, then it would have to be Sunday – but previously we proved
this wrong. Thus only the Lion spoke the truth when he met Alice on Thursday and
spoke with the Unicorn about Wednesday.