# construct a state space
stateSpace <- c("a", "b", "c")

# construct credal sets with the given state space
c <- credal(c(0.1, 0.1, 0.1), c(0.8, 0.8, 0.8), stateSpace) 

# extract first and second extreme point
c[1:2,]

# mass functions 
m <- mass(list("a"=0.1, "b"=0.1 , "c"=0.4, "a/b/c"=0.4), stateSpace)  

# extract focal elements
m[c("a","a/b/c")]