Alice,lion and the wonderland
Alice is walking through the forest of forgetfulness. She wants to know what day of the week it is. She stops and asks a lion and a unicorn. Now the lion lies all of the time on Monday, Tuesday and Wednesday. The unicorn always lies on Thursday, Friday and Saturday. Alice asks the lion what day it is he says "Well yesterday was one of my lying days." Alice cant figure it out just from the lions answer so she asks the unicorn and the unicorn says "Yesterday was also one of my lying days." What day is it?
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5 solutions
If today is one of the lion's "truth-telling" days then it must be Thursday, as this is the only truth-telling day preceded by a "lying" day.
If today is one of the lion's lying days then it must be Monday, as this is the only lying day preceded by a truth-telling day. So from the lion's response Alice knows that today is either Thursday or Monday.
By the same reasoning as above, if today is one of the unicorn's truth-telling days then it must be Sunday, and if it one of its lying days it must be Thursday. Thus for both the lion's and unicorn's statements to be consistent Alice must conclude that today is T h u r s d a y .