Alice came across a lion and a unicorn in a forest of forgetfulness. Those two are strange beings. The lion lies every Monday, Tuesday and Wednesday and the other days he speaks the truth. The unicorn lies on Thursdays, Fridays and Saturdays, however the other days of the week he speaks the truth.
Lion: Yesterday I was lying.
Unicorn: So was I.
On which day did they say that?
They said that on Thursday.
As there is no day when both 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.