He looked over her little tray of offerings, hiding a smile. He gravely selected a bright green glossy leaf and a bottle of water, and she opened it for him when the screw top lid confused him a little. "I would be pleased if you would summon me again. I shall spend time with you and teach you geometry, astronomy, and the theory of music over the next ten years when called upon to do so. In exchange as your payment to me you shall vow to never summon me in a manner that imprisons or constrains me against my will, to never knowingly aid an angel, and to learn Dark magic spells from me."