module Family where

-- We are given a child->parent relation as a non-deterministic function from
-- children to parents. E.g., George's parents are Elizabeth and Henry.
parent :: String -> String
parent "George" = "Elizabeth" ? "Henry"
parent "Fiona" = "Elizabeth" ? "Henry"
parent "Mary" = "Theresa" ? "Henry"
parent "Frederick" = "Theresa" ? "Francis"

-- Find the siblings of the input person.
-- Definition: y is a sibling of x iff x/=y and someone is a parent of both.
-- Duplicate answers are OK, e.g., sibling "George" gives "Fiona" twice because
-- of Elizabeth and Henry.
sibling :: String -> String
sibling = error "TODO"