skade88 writes: From the article 'Is the nature of a vacuum really fixed? Not so, according to two forthcoming papers. Researchers have identified a quantum level mechanism for interpreting a vacuum as being filled with pairs of virtual particles with fluctuating energy values. They've also discovered that physical constraints, such as the speed of light and the so-called impedance of free space, are indications of the total number of elementary particles in nature.'
egrep patterns are full regular expressions; it uses a fast deterministic
algorithm that sometimes needs exponential space.
-- unix manuals