Comment by reuben364

I just wrote redef to emphasize that I'm not shadowing the original definition.

    def a := 1
    def f x := a * x
    -- at this point f 1 evaluates to 1
    redef a := 2
    -- at this point f 1 evaluates to 2

But with dependent types, types can depend on prior values (in the previous example the type of x depends on the value t in the most direct way possible, as the type of x is t). If you redefine values, the subsequent definitions may not type-check anymore.