Primitive recursion is a well known syntactic restriction on recursive deenitions which guarantees termination. Unfortunately many natural deenitions, such as the most common deenition of Euclid's GCD algorithm, are not primitive recursive. Walther has recently given a proof system for verifying termination of a broader class of deenitions. Although Walther's system is highly automatible, the c...

Accumulation of bioactive compounds, during developmental stages of Graptopetalum paraguayense E. Walther, was investigated between 30 and 90days as a function of physiological maturity. Three distinct phases were defined: immature phase (30days), intermediate developmental phase (30-60days), and maturation phase (60-90days). Gallic acid and quercetin, antioxidative bioactive compounds, were id...

No problem is ever permanently closed. The editor is always pleased to consider for publication new solutions or new insights o n p a s t p r oblems.