Statement: 'Some chairs are curtains. All curtains are bed sheets.' Conclusion: 'Some chairs are bed sheets.' What is the mood of this syllogism?

Reading the three propositions in turn gives the pattern I, A, I.

'Some chairs are curtains' is a particular affirmative, coded I.

'All curtains are bed sheets' is a universal affirmative, coded A.

'Some chairs are bed sheets' is again a particular affirmative, coded I.

The mood is the ordered string of these quality-quantity codes, hence IAI.