KJ-4 Convert typed expressions into expressions with casts .
1. Cleaned up a bit the rules for lookup and loc. Eliminated some redundancies.
2. Studied the possibility to eliminate the type from lookup(L)::T.
Answer: lookup(L)::T have to stay like this after we'll finish elimination of TypedExp.
  In fact this will be the only typed expression left. In the end, when all other typed expressions will be removed,
  we can replace lookup(L)::T with lookup(L,T)