Ejemplo n.º 1
0
environment mk_rec_on(environment const & env, name const & n) {
    if (!inductive::is_inductive_decl(env, n))
        throw exception(sstream() << "error in 'rec_on' generation, '" << n << "' is not an inductive datatype");
    name rec_on_name(n, "rec_on");
    name_generator ngen;
    declaration rec_decl = env.get(inductive::get_elim_name(n));

    buffer<expr> locals;
    expr rec_type = rec_decl.get_type();
    while (is_pi(rec_type)) {
        expr local = mk_local(ngen.next(), binding_name(rec_type), binding_domain(rec_type), binding_info(rec_type));
        rec_type   = instantiate(binding_body(rec_type), local);
        locals.push_back(local);
    }

    // locals order
    //   A C minor_premises indices major-premise

    // new_locals order
    //   A C indices major-premise minor-premises
    buffer<expr> new_locals;
    unsigned idx_major_sz = *inductive::get_num_indices(env, n) + 1;
    unsigned minor_sz     = *inductive::get_num_minor_premises(env, n);
    unsigned AC_sz        = locals.size() - minor_sz - idx_major_sz;
    for (unsigned i = 0; i < AC_sz; i++)
        new_locals.push_back(locals[i]);
    for (unsigned i = 0; i < idx_major_sz; i++)
        new_locals.push_back(locals[AC_sz + minor_sz + i]);
    unsigned rec_on_major_idx = new_locals.size() - 1;
    for (unsigned i = 0; i < minor_sz; i++)
        new_locals.push_back(locals[AC_sz + i]);
    expr rec_on_type = Pi(new_locals, rec_type);

    levels ls = param_names_to_levels(rec_decl.get_univ_params());
    expr rec  = mk_constant(rec_decl.get_name(), ls);
    expr rec_on_val = Fun(new_locals, mk_app(rec, locals));

    bool use_conv_opt = true;
    environment new_env = module::add(env,
                                      check(env, mk_definition(env, rec_on_name, rec_decl.get_univ_params(),
                                                               rec_on_type, rec_on_val, use_conv_opt)));
    new_env = set_reducible(new_env, rec_on_name, reducible_status::Reducible);
    new_env = add_unfold_hint(new_env, rec_on_name, rec_on_major_idx);
    new_env = add_aux_recursor(new_env, rec_on_name);
    return add_protected(new_env, rec_on_name);
}
Ejemplo n.º 2
0
static environment mk_below(environment const & env, name const & n, bool ibelow) {
    if (!is_recursive_datatype(env, n))
        return env;
    if (is_inductive_predicate(env, n))
        return env;
    inductive::inductive_decls decls = *inductive::is_inductive_decl(env, n);
    type_checker tc(env);
    name_generator ngen;
    unsigned nparams       = std::get<1>(decls);
    declaration ind_decl   = env.get(n);
    declaration rec_decl   = env.get(inductive::get_elim_name(n));
    unsigned nindices      = *inductive::get_num_indices(env, n);
    unsigned nminors       = *inductive::get_num_minor_premises(env, n);
    unsigned ntypeformers  = length(std::get<2>(decls));
    level_param_names lps  = rec_decl.get_univ_params();
    bool is_reflexive      = is_reflexive_datatype(tc, n);
    level  lvl             = mk_param_univ(head(lps));
    levels lvls            = param_names_to_levels(tail(lps));
    level_param_names blvls; // universe level parameters of ibelow/below
    level  rlvl;  // universe level of the resultant type
    // The arguments of below (ibelow) are the ones in the recursor - minor premises.
    // The universe we map to is also different (l+1 for below of reflexive types) and (0 fo ibelow).
    expr ref_type;
    expr Type_result;
    if (ibelow) {
        // we are eliminating to Prop
        blvls      = tail(lps);
        rlvl       = mk_level_zero();
        ref_type   = instantiate_univ_param(rec_decl.get_type(), param_id(lvl), mk_level_zero());
    } else if (is_reflexive) {
        blvls = lps;
        rlvl  = get_datatype_level(ind_decl.get_type());
        // if rlvl is of the form (max 1 l), then rlvl <- l
        if (is_max(rlvl) && is_one(max_lhs(rlvl)))
            rlvl = max_rhs(rlvl);
        rlvl       = mk_max(mk_succ(lvl), rlvl);
        ref_type   = instantiate_univ_param(rec_decl.get_type(), param_id(lvl), mk_succ(lvl));
    } else {
        // we can simplify the universe levels for non-reflexive datatypes
        blvls       = lps;
        rlvl        = mk_max(mk_level_one(), lvl);
        ref_type    = rec_decl.get_type();
    }
    Type_result        = mk_sort(rlvl);
    buffer<expr> ref_args;
    to_telescope(ngen, ref_type, ref_args);
    if (ref_args.size() != nparams + ntypeformers + nminors + nindices + 1)
        throw_corrupted(n);

    // args contains the below/ibelow arguments
    buffer<expr> args;
    buffer<name> typeformer_names;
    // add parameters and typeformers
    for (unsigned i = 0; i < nparams; i++)
        args.push_back(ref_args[i]);
    for (unsigned i = nparams; i < nparams + ntypeformers; i++) {
        args.push_back(ref_args[i]);
        typeformer_names.push_back(mlocal_name(ref_args[i]));
    }
    // we ignore minor premises in below/ibelow
    for (unsigned i = nparams + ntypeformers + nminors; i < ref_args.size(); i++)
        args.push_back(ref_args[i]);

    // We define below/ibelow using the recursor for this type
    levels rec_lvls       = cons(mk_succ(rlvl), lvls);
    expr rec              = mk_constant(rec_decl.get_name(), rec_lvls);
    for (unsigned i = 0; i < nparams; i++)
        rec = mk_app(rec, args[i]);
    // add type formers
    for (unsigned i = nparams; i < nparams + ntypeformers; i++) {
        buffer<expr> targs;
        to_telescope(ngen, mlocal_type(args[i]), targs);
        rec = mk_app(rec, Fun(targs, Type_result));
    }
    // add minor premises
    for (unsigned i = nparams + ntypeformers; i < nparams + ntypeformers + nminors; i++) {
        expr minor = ref_args[i];
        expr minor_type = mlocal_type(minor);
        buffer<expr> minor_args;
        minor_type = to_telescope(ngen, minor_type, minor_args);
        buffer<expr> prod_pairs;
        for (expr & minor_arg : minor_args) {
            buffer<expr> minor_arg_args;
            expr minor_arg_type = to_telescope(tc, mlocal_type(minor_arg), minor_arg_args);
            if (is_typeformer_app(typeformer_names, minor_arg_type)) {
                expr fst  = mlocal_type(minor_arg);
                minor_arg = update_mlocal(minor_arg, Pi(minor_arg_args, Type_result));
                expr snd = Pi(minor_arg_args, mk_app(minor_arg, minor_arg_args));
                prod_pairs.push_back(mk_prod(tc, fst, snd, ibelow));
            }
        }
        expr new_arg = foldr([&](expr const & a, expr const & b) { return mk_prod(tc, a, b, ibelow); },
                             [&]() { return mk_unit(rlvl, ibelow); },
                             prod_pairs.size(), prod_pairs.data());
        rec = mk_app(rec, Fun(minor_args, new_arg));
    }

    // add indices and major premise
    for (unsigned i = nparams + ntypeformers; i < args.size(); i++) {
        rec = mk_app(rec, args[i]);
    }

    name below_name  = ibelow ? name{n, "ibelow"} : name{n, "below"};
    expr below_type  = Pi(args, Type_result);
    expr below_value = Fun(args, rec);

    bool use_conv_opt = true;
    declaration new_d = mk_definition(env, below_name, blvls, below_type, below_value,
                                      use_conv_opt);
    environment new_env = module::add(env, check(env, new_d));
    new_env = set_reducible(new_env, below_name, reducible_status::Reducible);
    if (!ibelow)
        new_env = add_unfold_hint(new_env, below_name, nparams + nindices + ntypeformers);
    return add_protected(new_env, below_name);
}
Ejemplo n.º 3
0
static environment mk_brec_on(environment const & env, name const & n, bool ind) {
    if (!is_recursive_datatype(env, n))
        return env;
    if (is_inductive_predicate(env, n))
        return env;
    inductive::inductive_decls decls = *inductive::is_inductive_decl(env, n);
    type_checker tc(env);
    name_generator ngen;
    unsigned nparams       = std::get<1>(decls);
    declaration ind_decl   = env.get(n);
    declaration rec_decl   = env.get(inductive::get_elim_name(n));
    // declaration below_decl = env.get(name(n, ind ? "ibelow" : "below"));
    unsigned nindices      = *inductive::get_num_indices(env, n);
    unsigned nminors       = *inductive::get_num_minor_premises(env, n);
    unsigned ntypeformers  = length(std::get<2>(decls));
    level_param_names lps  = rec_decl.get_univ_params();
    bool is_reflexive      = is_reflexive_datatype(tc, n);
    level  lvl             = mk_param_univ(head(lps));
    levels lvls            = param_names_to_levels(tail(lps));
    level rlvl;
    level_param_names blps;
    levels blvls; // universe level parameters of brec_on/binduction_on
    // The arguments of brec_on (binduction_on) are the ones in the recursor - minor premises.
    // The universe we map to is also different (l+1 for below of reflexive types) and (0 fo ibelow).
    expr ref_type;
    if (ind) {
        // we are eliminating to Prop
        blps       = tail(lps);
        blvls      = lvls;
        rlvl       = mk_level_zero();
        ref_type   = instantiate_univ_param(rec_decl.get_type(), param_id(lvl), mk_level_zero());
    } else if (is_reflexive) {
        blps    = lps;
        blvls   = cons(lvl, lvls);
        rlvl    = get_datatype_level(ind_decl.get_type());
        // if rlvl is of the form (max 1 l), then rlvl <- l
        if (is_max(rlvl) && is_one(max_lhs(rlvl)))
            rlvl = max_rhs(rlvl);
        rlvl       = mk_max(mk_succ(lvl), rlvl);
        // inner_prod, inner_prod_intro, pr1, pr2 do not use the same universe levels for
        // reflective datatypes.
        ref_type   = instantiate_univ_param(rec_decl.get_type(), param_id(lvl), mk_succ(lvl));
    } else {
        // we can simplify the universe levels for non-reflexive datatypes
        blps        = lps;
        blvls       = cons(lvl, lvls);
        rlvl        = mk_max(mk_level_one(), lvl);
        ref_type    = rec_decl.get_type();
    }
    buffer<expr> ref_args;
    to_telescope(ngen, ref_type, ref_args);
    if (ref_args.size() != nparams + ntypeformers + nminors + nindices + 1)
        throw_corrupted(n);

    // args contains the brec_on/binduction_on arguments
    buffer<expr> args;
    buffer<name> typeformer_names;
    // add parameters and typeformers
    for (unsigned i = 0; i < nparams; i++)
        args.push_back(ref_args[i]);
    for (unsigned i = nparams; i < nparams + ntypeformers; i++) {
        args.push_back(ref_args[i]);
        typeformer_names.push_back(mlocal_name(ref_args[i]));
    }
    // add indices and major premise
    for (unsigned i = nparams + ntypeformers + nminors; i < ref_args.size(); i++)
        args.push_back(ref_args[i]);
    // create below terms (one per datatype)
    //    (below.{lvls} params type-formers)
    // Remark: it also creates the result type
    buffer<expr> belows;
    expr result_type;
    unsigned k = 0;
    for (auto const & decl : std::get<2>(decls)) {
        name const & n1 = inductive::inductive_decl_name(decl);
        if (n1 == n) {
            result_type = ref_args[nparams + k];
            for (unsigned i = nparams + ntypeformers + nminors; i < ref_args.size(); i++)
                result_type = mk_app(result_type, ref_args[i]);
        }
        k++;
        name bname = name(n1, ind ? "ibelow" : "below");
        expr below = mk_constant(bname, blvls);
        for (unsigned i = 0; i < nparams; i++)
            below = mk_app(below, ref_args[i]);
        for (unsigned i = nparams; i < nparams + ntypeformers; i++)
            below = mk_app(below, ref_args[i]);
        belows.push_back(below);
    }
    // create functionals (one for each type former)
    //     Pi idxs t, below idxs t -> C idxs t
    buffer<expr> Fs;
    name F_name("F");
    for (unsigned i = nparams, j = 0; i < nparams + ntypeformers; i++, j++) {
        expr const & C = ref_args[i];
        buffer<expr> F_args;
        to_telescope(ngen, mlocal_type(C), F_args);
        expr F_result = mk_app(C, F_args);
        expr F_below  = mk_app(belows[j], F_args);
        F_args.push_back(mk_local(ngen.next(), "f", F_below, binder_info()));
        expr F_type   = Pi(F_args, F_result);
        expr F        = mk_local(ngen.next(), F_name.append_after(j+1), F_type, binder_info());
        Fs.push_back(F);
        args.push_back(F);
    }

    // We define brec_on/binduction_on using the recursor for this type
    levels rec_lvls       = cons(rlvl, lvls);
    expr rec              = mk_constant(rec_decl.get_name(), rec_lvls);
    // add parameters to rec
    for (unsigned i = 0; i < nparams; i++)
        rec = mk_app(rec, ref_args[i]);
    // add type formers to rec
    //     Pi indices t, prod (C ... t) (below ... t)
    for (unsigned i = nparams, j = 0; i < nparams + ntypeformers; i++, j++) {
        expr const & C = ref_args[i];
        buffer<expr> C_args;
        to_telescope(ngen, mlocal_type(C), C_args);
        expr C_t     = mk_app(C, C_args);
        expr below_t = mk_app(belows[j], C_args);
        expr prod    = mk_prod(tc, C_t, below_t, ind);
        rec = mk_app(rec, Fun(C_args, prod));
    }
    // add minor premises to rec
    for (unsigned i = nparams + ntypeformers, j = 0; i < nparams + ntypeformers + nminors; i++, j++) {
        expr minor = ref_args[i];
        expr minor_type = mlocal_type(minor);
        buffer<expr> minor_args;
        minor_type = to_telescope(ngen, minor_type, minor_args);
        buffer<expr> pairs;
        for (expr & minor_arg : minor_args) {
            buffer<expr> minor_arg_args;
            expr minor_arg_type = to_telescope(tc, mlocal_type(minor_arg), minor_arg_args);
            if (auto k = is_typeformer_app(typeformer_names, minor_arg_type)) {
                buffer<expr> C_args;
                get_app_args(minor_arg_type, C_args);
                expr new_minor_arg_type = mk_prod(tc, minor_arg_type, mk_app(belows[*k], C_args), ind);
                minor_arg = update_mlocal(minor_arg, Pi(minor_arg_args, new_minor_arg_type));
                if (minor_arg_args.empty()) {
                    pairs.push_back(minor_arg);
                } else {
                    expr r = mk_app(minor_arg, minor_arg_args);
                    expr r_1 = Fun(minor_arg_args, mk_pr1(tc, r, ind));
                    expr r_2 = Fun(minor_arg_args, mk_pr2(tc, r, ind));
                    pairs.push_back(mk_pair(tc, r_1, r_2, ind));
                }
            }
        }
        expr b = foldr([&](expr const & a, expr const & b) { return mk_pair(tc, a, b, ind); },
                       [&]() { return mk_unit_mk(rlvl, ind); },
                       pairs.size(), pairs.data());
        unsigned F_idx = *is_typeformer_app(typeformer_names, minor_type);
        expr F = Fs[F_idx];
        buffer<expr> F_args;
        get_app_args(minor_type, F_args);
        F_args.push_back(b);
        expr new_arg = mk_pair(tc, mk_app(F, F_args), b, ind);
        rec = mk_app(rec, Fun(minor_args, new_arg));
    }
    // add indices and major to rec
    for (unsigned i = nparams + ntypeformers + nminors; i < ref_args.size(); i++)
        rec = mk_app(rec, ref_args[i]);


    name brec_on_name  = name(n, ind ? "binduction_on" : "brec_on");
    expr brec_on_type  = Pi(args, result_type);
    expr brec_on_value = Fun(args, mk_pr1(tc, rec, ind));

    bool use_conv_opt = true;
    declaration new_d = mk_definition(env, brec_on_name, blps, brec_on_type, brec_on_value,
                                      use_conv_opt);
    environment new_env = module::add(env, check(env, new_d));
    new_env = set_reducible(new_env, brec_on_name, reducible_status::Reducible);
    if (!ind)
        new_env = add_unfold_hint(new_env, brec_on_name, nparams + nindices + ntypeformers);
    return add_protected(new_env, brec_on_name);
}
Ejemplo n.º 4
0
optional<environment> mk_no_confusion_type(environment const & env, name const & n) {
    optional<inductive::inductive_decls> decls = inductive::is_inductive_decl(env, n);
    if (!decls)
        throw exception(sstream() << "error in 'no_confusion' generation, '" << n << "' is not an inductive datatype");
    if (is_inductive_predicate(env, n))
        return optional<environment>(); // type is a proposition
    name_generator ngen;
    unsigned nparams       = std::get<1>(*decls);
    declaration ind_decl   = env.get(n);
    declaration cases_decl = env.get(name(n, "cases_on"));
    level_param_names lps  = cases_decl.get_univ_params();
    level  rlvl            = mk_param_univ(head(lps));
    levels ilvls           = param_names_to_levels(tail(lps));
    if (length(ilvls) != length(ind_decl.get_univ_params()))
        return optional<environment>(); // type does not have only a restricted eliminator
    expr ind_type          = instantiate_type_univ_params(ind_decl, ilvls);
    name eq_name("eq");
    name heq_name("heq");
    // All inductive datatype parameters and indices are arguments
    buffer<expr> args;
    ind_type = to_telescope(ngen, ind_type, args, some(mk_implicit_binder_info()));
    if (!is_sort(ind_type) || args.size() < nparams)
        throw_corrupted(n);
    lean_assert(!(env.impredicative() && is_zero(sort_level(ind_type))));
    unsigned nindices      = args.size() - nparams;
    // Create inductive datatype
    expr I = mk_app(mk_constant(n, ilvls), args);
    // Add (P : Type)
    expr P = mk_local(ngen.next(), "P", mk_sort(rlvl), binder_info());
    args.push_back(P);
    // add v1 and v2 elements of the inductive type
    expr v1 = mk_local(ngen.next(), "v1", I, binder_info());
    expr v2 = mk_local(ngen.next(), "v2", I, binder_info());
    args.push_back(v1);
    args.push_back(v2);
    expr R  = mk_sort(rlvl);
    name no_confusion_type_name{n, "no_confusion_type"};
    expr no_confusion_type_type = Pi(args, R);
    // Create type former
    buffer<expr> type_former_args;
    for (unsigned i = nparams; i < nparams + nindices; i++)
        type_former_args.push_back(args[i]);
    type_former_args.push_back(v1);
    expr type_former = Fun(type_former_args, R);
    // Create cases_on
    levels clvls   = levels(mk_succ(rlvl), ilvls);
    expr cases_on  = mk_app(mk_app(mk_constant(cases_decl.get_name(), clvls), nparams, args.data()), type_former);
    cases_on       = mk_app(cases_on, nindices, args.data() + nparams);
    expr cases_on1 = mk_app(cases_on, v1);
    expr cases_on2 = mk_app(cases_on, v2);
    type_checker tc(env);
    expr t1        = tc.infer(cases_on1).first;
    expr t2        = tc.infer(cases_on2).first;
    buffer<expr> outer_cases_on_args;
    unsigned idx1 = 0;
    while (is_pi(t1)) {
        buffer<expr> minor1_args;
        expr minor1 = to_telescope(tc, binding_domain(t1), minor1_args);
        expr curr_t2  = t2;
        buffer<expr> inner_cases_on_args;
        unsigned idx2 = 0;
        while (is_pi(curr_t2)) {
            buffer<expr> minor2_args;
            expr minor2 = to_telescope(tc, binding_domain(curr_t2), minor2_args);
            if (idx1 != idx2) {
                // infeasible case, constructors do not match
                inner_cases_on_args.push_back(Fun(minor2_args, P));
            } else {
                if (minor1_args.size() != minor2_args.size())
                    throw_corrupted(n);
                buffer<expr> rtype_hyp;
                // add equalities
                for (unsigned i = 0; i < minor1_args.size(); i++) {
                    expr lhs      = minor1_args[i];
                    expr rhs      = minor2_args[i];
                    expr lhs_type = mlocal_type(lhs);
                    expr rhs_type = mlocal_type(rhs);
                    level l       = sort_level(tc.ensure_type(lhs_type).first);
                    expr h_type;
                    if (tc.is_def_eq(lhs_type, rhs_type).first) {
                        h_type = mk_app(mk_constant(eq_name, to_list(l)), lhs_type, lhs, rhs);
                    } else {
                        h_type = mk_app(mk_constant(heq_name, to_list(l)), lhs_type, lhs, rhs_type, rhs);
                    }
                    rtype_hyp.push_back(mk_local(ngen.next(), local_pp_name(lhs).append_after("_eq"), h_type, binder_info()));
                }
                inner_cases_on_args.push_back(Fun(minor2_args, mk_arrow(Pi(rtype_hyp, P), P)));
            }
            idx2++;
            curr_t2 = binding_body(curr_t2);
        }
        outer_cases_on_args.push_back(Fun(minor1_args, mk_app(cases_on2, inner_cases_on_args)));
        idx1++;
        t1 = binding_body(t1);
    }
    expr no_confusion_type_value = Fun(args, mk_app(cases_on1, outer_cases_on_args));

    bool opaque       = false;
    bool use_conv_opt = true;
    declaration new_d = mk_definition(env, no_confusion_type_name, lps, no_confusion_type_type, no_confusion_type_value,
                                      opaque, ind_decl.get_module_idx(), use_conv_opt);
    environment new_env = module::add(env, check(env, new_d));
    return some(add_protected(new_env, no_confusion_type_name));
}
Ejemplo n.º 5
0
environment mk_no_confusion(environment const & env, name const & n) {
    optional<environment> env1 = mk_no_confusion_type(env, n);
    if (!env1)
        return env;
    environment new_env = *env1;
    type_checker tc(new_env);
    inductive::inductive_decls decls   = *inductive::is_inductive_decl(new_env, n);
    unsigned nparams                   = std::get<1>(decls);
    name_generator ngen;
    declaration no_confusion_type_decl = new_env.get(name{n, "no_confusion_type"});
    declaration cases_decl             = new_env.get(name(n, "cases_on"));
    level_param_names lps              = no_confusion_type_decl.get_univ_params();
    levels ls                          = param_names_to_levels(lps);
    expr no_confusion_type_type        = instantiate_type_univ_params(no_confusion_type_decl, ls);
    name eq_name("eq");
    name heq_name("heq");
    name eq_refl_name{"eq", "refl"};
    name heq_refl_name{"heq", "refl"};
    buffer<expr> args;
    expr type = no_confusion_type_type;
    type = to_telescope(ngen, type, args, some(mk_implicit_binder_info()));
    lean_assert(args.size() >= nparams + 3);
    unsigned nindices = args.size() - nparams - 3; // 3 is for P v1 v2
    expr range        = mk_app(mk_constant(no_confusion_type_decl.get_name(), ls), args);
    expr P            = args[args.size()-3];
    expr v1           = args[args.size()-2];
    expr v2           = args[args.size()-1];
    expr v_type       = mlocal_type(v1);
    level v_lvl       = sort_level(tc.ensure_type(v_type).first);
    expr eq_v         = mk_app(mk_constant(eq_name, to_list(v_lvl)), v_type);
    expr H12          = mk_local(ngen.next(), "H12", mk_app(eq_v, v1, v2), binder_info());
    args.push_back(H12);
    name no_confusion_name{n, "no_confusion"};
    expr no_confusion_ty = Pi(args, range);
    // The gen proof is of the form
    //   (fun H11 : v1 = v1, cases_on Params (fun Indices v1, no_confusion_type Params Indices P v1 v1) Indices v1
    //        <for-each case>
    //        (fun H : (equations -> P), H (refl) ... (refl))
    //        ...
    //   )

    // H11 is for creating the generalization
    expr H11          = mk_local(ngen.next(), "H11", mk_app(eq_v, v1, v1), binder_info());
    // Create the type former (fun Indices v1, no_confusion_type Params Indices P v1 v1)
    buffer<expr> type_former_args;
    for (unsigned i = nparams; i < nparams + nindices; i++)
        type_former_args.push_back(args[i]);
    type_former_args.push_back(v1);
    buffer<expr> no_confusion_type_args;
    for (unsigned i = 0; i < nparams + nindices; i++)
        no_confusion_type_args.push_back(args[i]);
    no_confusion_type_args.push_back(P);
    no_confusion_type_args.push_back(v1);
    no_confusion_type_args.push_back(v1);
    expr no_confusion_type_app = mk_app(mk_constant(no_confusion_type_decl.get_name(), ls), no_confusion_type_args);
    expr type_former = Fun(type_former_args, no_confusion_type_app);
    // create cases_on
    levels clvls   = ls;
    expr cases_on  = mk_app(mk_app(mk_constant(cases_decl.get_name(), clvls), nparams, args.data()), type_former);
    cases_on       = mk_app(mk_app(cases_on, nindices, args.data() + nparams), v1);
    expr cot       = tc.infer(cases_on).first;

    while (is_pi(cot)) {
        buffer<expr> minor_args;
        expr minor = to_telescope(tc, binding_domain(cot), minor_args);
        lean_assert(!minor_args.empty());
        expr H  = minor_args.back();
        expr Ht = mlocal_type(H);
        buffer<expr> refl_args;
        while (is_pi(Ht)) {
            buffer<expr> eq_args;
            expr eq_fn = get_app_args(binding_domain(Ht), eq_args);
            if (const_name(eq_fn) == eq_name) {
                refl_args.push_back(mk_app(mk_constant(eq_refl_name, const_levels(eq_fn)), eq_args[0], eq_args[1]));
            } else {
                refl_args.push_back(mk_app(mk_constant(heq_refl_name, const_levels(eq_fn)), eq_args[0], eq_args[1]));
            }
            Ht = binding_body(Ht);
        }
        expr pr  = mk_app(H, refl_args);
        cases_on = mk_app(cases_on, Fun(minor_args, pr));
        cot = binding_body(cot);
    }
    expr gen = Fun(H11, cases_on);
    // Now, we use gen to build the final proof using eq.rec
    //
    //  eq.rec InductiveType v1 (fun (a : InductiveType), v1 = a -> no_confusion_type Params Indices v1 a) gen v2 H12 H12
    //
    name eq_rec_name{"eq", "rec"};
    expr eq_rec = mk_app(mk_constant(eq_rec_name, {head(ls), v_lvl}), v_type, v1);
    // create eq_rec type_former
    //    (fun (a : InductiveType), v1 = a -> no_confusion_type Params Indices v1 a)
    expr a   = mk_local(ngen.next(), "a",   v_type, binder_info());
    expr H1a = mk_local(ngen.next(), "H1a", mk_app(eq_v, v1, a), binder_info());
    // reusing no_confusion_type_args... we just replace the last argument with a
    no_confusion_type_args.pop_back();
    no_confusion_type_args.push_back(a);
    expr no_confusion_type_app_1a = mk_app(mk_constant(no_confusion_type_decl.get_name(), ls), no_confusion_type_args);
    expr rec_type_former = Fun(a, Pi(H1a, no_confusion_type_app_1a));
    // finalize eq_rec
    eq_rec = mk_app(mk_app(eq_rec, rec_type_former, gen, v2, H12), H12);
    //
    expr no_confusion_val = Fun(args, eq_rec);

    bool opaque       = false;
    bool use_conv_opt = true;
    declaration new_d = mk_definition(new_env, no_confusion_name, lps, no_confusion_ty, no_confusion_val,
                                      opaque, no_confusion_type_decl.get_module_idx(), use_conv_opt);
    new_env = module::add(new_env, check(new_env, new_d));
    return add_protected(new_env, no_confusion_name);
}