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Syrus
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Homework Statement
If a subset (call it B) of a partially ordered (by a relation R) set A has exactly one minimal element, must that element be a smallest element? Give proof or counterexample.
Homework Equations
Well, our given, "exactly one minimal element" in PC (pred calc.) translates to:
(∃b)((∀x)((x,b) ∈ R → x = b) ∧ (∀y)((∀z)((z,y) ∈ R → b = y))
i hope...
The Attempt at a Solution
Call b the unique minimal element of B and let k ∈ B. Since (k,k) ∈ R, then using our assumption (∀y)((∀z)((z,y) ∈ R → b = y), b = k. Thus, (b,k) ∈ R.
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