# 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) 

# replace first and second extreme point
c[1:2,] <- rbind(c(0.1, 0.1, 0.8), c(0.2, 0.2, 0.6))

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

# switch mass on focal elements "b" and "a/b/c" 
temp <- m["b"]
m["b"] <- m["a/b/c"]
m["a/b/c"] <- temp