Simulates Strauss spatial point process.

Syntax
	Strauss(n, c=0, r)
Input 
n  number of points
c  parameter `c' in [0, 1]. `c' = 0 corresponds to complete inhibition at
distances up to `r'.
 r  inhibition distance

Output
list of vectors of x and y coordinates

Side effects
uses the random number generator

Details
Uses spatial birth-and-death process for 4`n' steps, or for 40`n' steps
starting from a binomial pattern on the first call from an other function.
Uses the region set by `ppinit' or `ppregion'.

See also
`Psim', `SSI'

Examples
towns <- ppinit("towns.dat")
par(pty="s")
plot(Kfn(towns, 10), type="b", xlab="distance", ylab="L(t)")
lines(Kaver(10, 25, Strauss(69,0.5,3.5)))