问题描述：
请教一道离散数学题
Find a common universe for variables x, y, z, w for which the statement
∀x∀y∀z∃w ((w≠x)∧(w≠ y)∧(w≠z))
is true and another common universe for these variables in which it is
false.
Find a common universe for variables x, y, z, w for which the statement
∀x∀y∀z∃w ((w≠x)∧(w≠ y)∧(w≠z))
is true and another common universe for these variables in which it is
false.
问题解答：
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