There are three people (Xavier, Yani, and Zena), one of whom is a doctor, one a lawyer, and one a plumber. The doctor always tells the truth, the lawyer always lies, and the plumber can either lie or tell the truth.
Xavier says: "Zena is a lawyer"
Yani says: "Xavier is a doctor"
Zena says: "I am the plumber"
Who is the doctor, who is the lawyer, and who is the plumber?
Xavier says: "Zena is a lawyer"
Yani says: "Xavier is a doctor"
Zena says: "I am the plumber"
Who is the doctor, who is the lawyer, and who is the plumber?