Development of a structured program for conversion to prenex normal form

The method of structured programming or program development using a top-down, stepwise refinement technique provides a systematic approach for the development of programs of considerable complexity. The aim of this paper is to present the philosophy of structured programming through a case study of a nonnumeric programming task. The problem of converting a well-formed formula in first-order logic into prenex normal form is considered. The program has been coded in the programming language PASCAL and implemented on a DEC-10 system. The program has about 500 lines of code and comprises 11 procedures.

A computational algorithm for the verification of tautologies in propositional calculus

A computational algorithm (based on Smullyan's analytic tableau method) that varifies whether a given well-formed formula in propositional calculus is a tautology or not has been implemented on a DEC system 10. The stepwise refinement approch of program development used for this implementation forms the subject matter of this paper. The top-down design has resulted in a modular and reliable program package. This computational algoritlhm compares favourably with the algorithm based on the well-known resolution principle used in theorem provers.

Transcription factor erect wing (EWG) is involved in indirect flight muscle patterning, development and maintenance in Drosophila

Muscle development is a multistep process which includes myoblast diversification, proliferation, migration, fusion, differentiation and growth. A hierarchical exhibition of myogenic factors is important for dexterous execution of progressive events in muscle formation. EWG (erect wing) is a transcription factor known to have a role in indirect flight muscle development (IFM) in Drosophila. We marked out the precise spatio-temporal expression profile of EWG in the myoblasts, and in the developing muscles. Mutant adult flies null for EWG in myoblasts show variable number of IFM, suggesting that EWG is required for patterning of the IFM. The remnant muscle found in the EWG null flies show proper assembly of the structural proteins, which implies that some myoblasts manage to fuse, develop and differentiate normally indicating that EWG is not required for differentiation program per se. However, when EWG expression is extended beyond its expression window in a wild type background, muscle thinning is observed implying EWG function in protein synthesis inhibition. Mis-expression studies in wing disc myoblasts hinted at its role in myoblast proliferation. We thus conclude that EWG is important for regulating fusion events which in turn decides the IFM pattern. Also IFM in EWG null mutants show clumps containing broken fibres and an altered mitochondrial morphology. The vertebrate homolog of EWG is nuclear respiratory factor1 (NRF1) which is known to have a function in mitochondrial biogenesis and protection against oxidative stress. Gene expression for inner mitochondrial membrane protein, Opa1-like was found to be absent in these mutants. Also, these flies were more sensitive to oxidative stress, indicating a compromised mitochondrial functioning. Our results therefore demonstrate that EWG functions in maintaining muscles’ structural integrity by ensuing proper mitochondrial activity.