This Note Presents a Necessary and Sufficient Condition for All Goods to Be Normal, in the Case of Differentiable Individual Demand. This Condition Appears As a Relationship Between the Quantity Effects on Marginal Willingness to Pay and Is Consequently a Characteristic of the Preference Order....

In This Note, We Shall Demonstrate a Slight Extension of the Envelope Theorem and Use It to Prove That an Intertemporatl Economy Can Be Spanned Or Represented by a Sequence of Temporary Economies, Each of Them Preserving the Geometrical and Analytical Structure of the Previous One.