Let X and Z be topological spaces and Y be a subspace of X. A con-
tinuous function f : Y ! Z is extendable to X if there exists a continuous
function f : X ! Z such that f(x) = f(x) for all x 2 Y . If every continuous
function f : Y ! Z is...
Earth sheltered houses -- United States; Underground architecture -- United States; Underground construction
Subterranean housing has long been an integral part of human history. Naturally occurring underground spaces provided shelter for the earliest humans. Occupation of the subscape from 100 B.C. to present day exemplifies the significance of the...
In this paper Euclidean and hyperbolic discontinuous isometries* are discussed and compared. The graphic artist M.C. Escher (1898-1972) produced works which have for the structure points, lines, and angles, which repeat in the plane (Euclidean and...
