Terms-Software evolution,The difference equation determining evolutionary growth of (some) software systems is generalized to a differential one. A hypothetical geometric model is derived and its possible uses are illustrated.

The Concise Oxford Dictionary defines the adjective "reliable" as follows: that may be relied upon, of sound and consistent character of quality. Thus there are two distinct components of the notion: one, relating to the use, another to internal properties of the thing that is described as reliable. The author considers some consequences of blurring the distinction, or worse, of substituting one meaning for another.

Iterative computations are considered in this paper as a general problem-solving technique. The loop invariant is derived from problem properties rather than from program properties (as is usual in programming literature). To this end, the notion of equisolution states-a special subset of space-state in which lie the iterated trajectories-is introduced.

This paper describes, in a preliminary way, a model of data collection, patterned after sentential calculus. The purely syntactic character of the latter (Grzegorczyk, 1974), combined with recent advances in formal grammars (Deussen, 1975) seem to indicate how to push the confusing issues of semantics well outside the operational part of the system supporting such collection; at the same time, we get a total independence of any implementational factors. With today's notational technology it does not seem prohibitively difficult to develop completely the model proposed in this paper; it is felt, however, that the chosen form of presentation brings up the salient features of the idea uncluttered by a mass of details.

SODA is an operating system for a new Polish computer ODRA-1204. This paper gives an account of the basic principles of SODA structure and operation. SODA is an operating system for a small computer (without magnetic tapes) tailored to the needs of a research institute. A fundamental objective achieved by means of SODA is the simultaneous preparation and execution of programs.