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Abstract. We present the extended notion of pure exchange economy under uncertainty, called an economy with awareness structure, where each trader makes decision under his/her awareness and belief and has strictly monotone preferences. We show the no speculation theorem: If the initial endowment is ex-ante Pareto optimal then there exists no other expectations equilibrium in awareness for any price.

Abstract. We present the extended notion of pure exchange economy under uncertainty, called an economy with awareness structure, where each trader having a strictly monotone preference makes decision under his/her awareness and belief, and we introduce a generalized notion of equilibrium for the economy, called an expectations equilibrium in awareness. We show the existence theorem of the equilibrium and the fundamental welfare theorem for the economy, i.e., an allocation in the economy is ex-ante Pareto optimal if and only if it is an expectations equilibrium allocation in awareness.