This paper presents a proof-theoretical approach to the question "What is a logical constant?" This approach starts with the assumption that logic is the science of formal deductions, and that basic formal deductions are structural deductions, i.e. deductions independent of any constant of the language to which the premises and conclusions belong. Logical constants, on which the remaining forma...

The value of federal income-tax deductions, such as the home mortgage interest deduction (MID), varies across geographic regions. Taxpayers in regions with relatively high incomes, state and local income taxes, and housing costs are more likely to utilize deductions; that is, they are more likely to itemize, more likely to have a larger deduction conditional on itemizing, and more likely to get...

A Gentzen sequent calculus for Lax Logic is presented, the proofs in which naturally correspond in a 1–1 way with the normal natural deductions for the logic. The propositional fragment of this calculus is then used a basis for another calculus, one which uses a history mechanism in order to give a decision procedure for propositional Lax Logic.

The interpretation of strong double radio sources in terms of the "beam" model is reviewed. Implications of this model for source evolution and the nature of radio trails are briefly discussed. A final section is concerned with deductions about the properties of compact and variable components in quasars and galactic nuclei.

I present a new syntactical method for proving the Interpolation Theorem for the implicational fragment of intuitionistic logic and its substructural subsystems. This method, like Prawitz’s, works on natural deductions rather than sequent derivations, and, unlike existing methods, always finds a ‘strongest’ interpolant under a certain restricted but reasonable notion of what counts as an ‘inter...