xs        = [10, 20, 30]
xs[0]     = 10
xs[-1]    = 30
len(xs)   = 3
after push= [10, 20, 30, 40]
popped    = 40, now [10, 20, 30]
xs[1]=99  = [10, 99, 30]
spread    = [0, 10, 99, 30, 100]
concat    = [1, 2, 3, 4]
person[name]= Ada
person[age] = 36
computed    = two
has role? true
keys      = ["name", "age", 2, "role"]
values    = ["Ada", 36, "two", "engineer"]
after del = false
