If X + Y means “X is the daughter of Y”, X * Y means “X is the son of Y” and X-Y means “X is the wife of Y”, then in the expression “Z * T - S * U - P”, What is U to Z?

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If X + Y means “X is the daughter of Y”, X * Y means “X is the son of Y” and X-Y means “X is the wife of Y”, then in the expression “Z * T - S * U - P”, What is U to Z?
  
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