let s be a monoid and x a class of s-acts which is closed under coproducts. the object of this article is to find conditions under which all s-acts have x-precovering. we have shown that the existence of torsion-free precovering implies the existence of torsion-free covering. this work is an attempt to further facilitate the study of the conjecture that all s-acts have flat cover.

During the heroic age of Antarctic exploration, snow blindness was a common problem, but not all the descriptions of it fit the modern view of the disease, and some of the explorers complained of long-term problems. This article describes the snow blindness and other eye problems that occurred during this era. It also describes how snow blindness was prevented and treated.

We report the case of a 38-yr-old man who presented for an emergency mastoidectomy and suffered from severe upper airways obstruction in the postoperative period. Subsequent questioning revealed a history of heroic snoring and further investigations proved a diagnosis of obstructive sleep apnoea.

Traumatic cardiac arrest resuscitation is considered a heroic and futile endeavor. However, newer articles have more promising statistics and divide between prehospital ground and helicopter transport. Here we discuss why there might be a difference in the survivability of this subset of trauma patients.

SOFTWARE-INTENSIVE SYSTEMS with high reliability requirements typically are implemented through heroic (and expensive) engineering efforts. Control systems in planes, nuclear reactors, trains, pacemakers, and spaceships are developed by highly trained personnel through strictly managed software development processes with a dose of formal methods. This approach has worked admirably up to now, bu...