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  • Write the down the condition under which two feature values agree, and apply this to the two feature values {3s,3p} and {1s,2s,1p,2p,3p}.

    Answer: Two feature values unify by intersection, and they agree if they have non-empty intersection.
    {3s,3p} ∩ {1s,2s,1p,2p,3p} = {3p}, which is non-empty, so these two features agree.