local env = environment()
local nat = Const("nat")

env = add_inductive(env,
                    "nat", Type,
                    "zero", nat,
                    "succ", mk_arrow(nat, nat))

-- Display all declarations in the environment
env:for_each(function(d)
                print(tostring(d:name()) .. " : " .. tostring(d:type()))
             end
)