```
x <- runif(30)
y <- runif(30)
w <- ripras(x,y)
plot(owin(), main="ripras(x,y)")
plot(w, add=TRUE)
points(x,y)
X <- rpoispp(15)
plot(X, main="ripras(X)")
plot(ripras(X), add=TRUE)
# two points insufficient
ripras(c(0,1),c(0,0))
# triangle
ripras(c(0,1,0.5), c(0,0,1))
# three collinear points
ripras(c(0,0,0), c(0,1,2))
```

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