diff --git a/src/checker/CMakeLists.txt b/src/checker/CMakeLists.txt
index 203c1896cb..07eabbe296 100644
--- a/src/checker/CMakeLists.txt
+++ b/src/checker/CMakeLists.txt
@@ -1,4 +1,4 @@
-add_executable(leanchecker checker.cpp text_import.cpp
+add_executable(leanchecker checker.cpp text_import.cpp simple_pp.cpp
         $<TARGET_OBJECTS:util> $<TARGET_OBJECTS:sexpr>
         $<TARGET_OBJECTS:kernel> $<TARGET_OBJECTS:inductive> $<TARGET_OBJECTS:quotient>)
 target_link_libraries(leanchecker ${EXTRA_UTIL_LIBS})
diff --git a/src/checker/checker.cpp b/src/checker/checker.cpp
index d94298eb15..1925448d4d 100644
--- a/src/checker/checker.cpp
+++ b/src/checker/checker.cpp
@@ -14,6 +14,8 @@ Author: Gabriel Ebner
 #include "kernel/inductive/inductive.h"
 #include "kernel/standard_kernel.h"
 #include "checker/text_import.h"
+#include "checker/simple_pp.h"
+
 #if defined(LEAN_EMSCRIPTEN)
 #include <emscripten.h>
 #endif
@@ -41,8 +43,8 @@ int main(int argc, char ** argv) {
         });
 #endif
 
-    if (argc != 2) {
-        std::cout << "usage: leanchecker export.out" << std::endl;
+    if (argc < 2) {
+        std::cout << "usage: leanchecker export.out lemma_to_print" << std::endl;
         return 1;
     }
 
@@ -73,6 +75,22 @@ int main(int argc, char ** argv) {
         env = declare_quotient(env);
         import_from_text(in, env);
 
+        env.for_each_declaration([&] (declaration const & d) {
+            if (d.is_axiom()) {
+                std::cout << compose_many(
+                        {format("axiom"), space(), simple_pp(d.get_name()), space(), format(":"), space(),
+                         simple_pp(env, d.get_type()), line()});
+            }
+        });
+
+        for (int i = 2; i < argc; i++) {
+            name n = string_to_name(argv[i]);
+            auto d = env.get(n);
+            std::cout << compose_many(
+                    {format("theorem"), space(), simple_pp(d.get_name()), space(), format(":"), space(),
+                     simple_pp(env, d.get_type()), line()});
+        }
+
         unsigned num_decls = 0;
         env.for_each_declaration([&] (declaration const &) { num_decls++; });
         std::cout << "checked " << num_decls << " declarations" << std::endl;
diff --git a/src/checker/simple_pp.cpp b/src/checker/simple_pp.cpp
new file mode 100644
index 0000000000..8acb449fd3
--- /dev/null
+++ b/src/checker/simple_pp.cpp
@@ -0,0 +1,258 @@
+/*
+Copyright (c) 2017 Microsoft Corporation. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+
+Author: Gabriel Ebner
+*/
+#include "checker/simple_pp.h"
+#include "kernel/instantiate.h"
+#include "kernel/type_checker.h"
+#include "kernel/for_each_fn.h"
+
+namespace lean {
+
+format compose_many(std::initializer_list<format> const & fmts) {
+    format res;
+    bool first = true;
+    for (auto & fmt : fmts) {
+        if (first) {
+            res = fmt;
+            first = false;
+        } else {
+            res = compose(res, fmt);
+        }
+    }
+    return res;
+}
+
+static format pp_name(name n) {
+    bool last = true;
+    format fmt;
+    while (n) {
+        auto limb = n.is_numeral() ? format(n.get_numeral()) : format(n.get_string());
+        fmt = last ? limb : compose_many({limb, format("."), fmt});
+        last = false;
+        n = n.get_prefix();
+    }
+    return last ? format("[anonymous]") : fmt;
+}
+
+struct simple_pp_fn {
+    type_checker m_tc;
+    unsigned m_indent = 0;
+
+    simple_pp_fn(environment const & env) : m_tc(env) {}
+
+    static constexpr unsigned MAX_PRIO = 1024;
+    struct result {
+        format m_fmt;
+        unsigned m_prio;
+
+        result(format const & fmt, unsigned prio) : m_fmt(fmt), m_prio(prio) {}
+        result(format const & fmt) : m_fmt(fmt), m_prio(MAX_PRIO) {}
+
+        result maybe_paren() const { return maybe_paren(MAX_PRIO); }
+        result maybe_paren(unsigned new_prio) const {
+            if (m_prio < new_prio) {
+                return paren(m_fmt);
+            } else {
+                return *this;
+            }
+        }
+
+        operator format() const { return m_fmt; }
+    };
+
+    result pp_meta(name const & n) {
+        return compose(format("?"), pp_name(n));
+    }
+
+    result pp_level(level const & l) {
+        switch (l.kind()) {
+            case level_kind::Zero: return format("0");
+            case level_kind::Succ: return result(compose(pp_level(succ_of(l)).maybe_paren(1), format("+1")), 0);
+            case level_kind::Max:
+                return result(compose_many({format("max"), space(),
+                                            pp_level(max_lhs(l)).maybe_paren(1),
+                                            pp_level(max_rhs(l)).maybe_paren(1)}), 0);
+            case level_kind::IMax:
+                return result(compose_many({format("imax"), space(),
+                                            pp_level(imax_lhs(l)).maybe_paren(1),
+                                            pp_level(imax_rhs(l)).maybe_paren(1)}), 0);
+            case level_kind::Param: return pp_name(param_id(l));
+            case level_kind::Global: return pp_name(global_id(l));
+            case level_kind::Meta: return pp_meta(meta_id(l));
+        }
+        lean_unreachable();
+    }
+
+    result pp_var(expr const & e) {
+        return compose(format("#"), format(var_idx(e)));
+    }
+
+    result pp_sort(expr const & e) {
+        if (sort_level(e) == mk_level_zero()) {
+            return format("Prop");
+        } else if (sort_level(e) == mk_level_one()) {
+            return format("Type");
+        } else {
+            return compose_many({format("Type"), space(), pp_level(sort_level(e)).maybe_paren()});
+        }
+    }
+
+    result pp_const(expr const & e) {
+        return pp_name(const_name(e));
+    }
+
+    result pp_meta(expr const & e) {
+        return pp_meta(mlocal_name(e));
+    }
+
+    result pp_local(expr const & e) {
+        return pp_name(local_pp_name(e));
+    }
+
+    bool is_implicit(expr const & f) {
+        if (!closed(f)) {
+            // the Lean type checker assumes expressions are closed.
+            return false;
+        }
+        try {
+            expr t = m_tc.relaxed_whnf(m_tc.infer(f));
+            if (is_pi(t)) {
+                binder_info bi = binding_info(t);
+                return bi.is_implicit() || bi.is_strict_implicit() || bi.is_inst_implicit();
+            } else {
+                return false;
+            }
+        } catch (exception &) {
+            return false;
+        }
+    }
+
+    result pp_app(expr const & e) {
+        auto fn = get_app_fn(e);
+        format fmt = pp(fn).maybe_paren();
+        buffer<expr> args; get_app_args(e, args);
+        for (auto & arg : args) {
+            if (!is_implicit(fn)) {
+                fmt = compose_many({fmt, space(), pp(arg).maybe_paren()});
+            }
+            fn = mk_app(fn, arg);
+        }
+        return result(group(fmt), MAX_PRIO-1);
+    }
+
+    std::unordered_set<name, name_hash> used_names;
+    name get_unused(name n) {
+        if (!used_names.count(n)) return n;
+
+        n = n.get_subscript_base();
+        for (unsigned i = 1;; i++) {
+            auto n_i = n.append_after(i);
+            if (!used_names.count(n_i))
+                return n_i;
+        }
+    }
+
+    struct local_const {
+        simple_pp_fn * m_fn;
+        name m_pp_name;
+        expr m_lc;
+
+        local_const(simple_pp_fn * fn, name pp_name, expr const & domain, binder_info const & bi) : m_fn(fn) {
+            m_pp_name = m_fn->get_unused(pp_name);
+            m_fn->used_names.insert(m_pp_name);
+            m_lc = mk_local(m_pp_name, m_pp_name, domain, bi);
+            m_fn->m_tc.push_local(m_pp_name, domain, bi);
+        }
+        ~local_const() {
+            m_fn->used_names.erase(m_pp_name);
+            m_fn->m_tc.pop_local();
+        }
+
+        expr const & domain() const { return mlocal_type(m_lc); }
+
+        local_const(simple_pp_fn * fn, expr const & binder) :
+                local_const(fn, binding_name(binder), binding_domain(binder), binding_info(binder)) {}
+    };
+
+    void mark_used_const_names(expr const & e) {
+        for_each(e, [&] (expr const & c, unsigned) {
+            if (is_constant(c))
+                used_names.insert(const_name(c));
+            return true;
+        });
+    }
+
+    result pp_lambda(expr const & e) {
+        local_const lc(this, e);
+        return result(group(compose_many({format("λ"), space(), pp(lc.m_lc), space(), format(":"), space(),
+                                    pp(binding_domain(e)).maybe_paren(1), format(","),
+                                    space(), pp(instantiate(binding_body(e), lc.m_lc))})), 0);
+    }
+
+    result pp_pi(expr e) {
+        if (!has_free_vars(binding_body(e))) {
+            // implication
+            return result(group(compose_many({pp(binding_domain(e)).maybe_paren(25), space(), format("->"),
+                                              space(), pp(binding_body(e)).maybe_paren(24)})), 24);
+        } else {
+            buffer<local_const> lcs;
+            do {
+                lcs.emplace_back(this, e);
+                e = instantiate(binding_body(e), lcs.back().m_lc);
+            } while (is_pi(e) && has_free_vars(binding_body(e)) &&
+                    m_tc.is_def_eq(lcs.back().domain(), binding_domain(e)));
+
+            auto fmt = format("Π");
+            for (auto & lc : lcs)
+                fmt = compose_many({fmt, space(), pp_name(lc.m_pp_name)});
+
+            fmt = compose_many({fmt, space(), format(":"), space(),
+
+                                pp(lcs.back().domain()).maybe_paren(1), format(","),
+                                space(), pp(e)});
+            return result(group(fmt), 0);
+        }
+    }
+
+    result pp_macro(expr const &) {
+        return format("[macro]");
+    }
+
+    result pp_let(expr const & e) {
+        local_const lc(this, let_name(e), let_type(e), binder_info());
+        return result(group(compose_many({format("let"), space(), pp(lc.m_lc), space(), format(":"), space(),
+                                    pp(let_type(e)).maybe_paren(1), space(), format(":="), space(), pp(let_value(e)), format(","),
+                                    space(), pp(instantiate(let_body(e), lc.m_lc))})), 0);
+    }
+
+    result pp(expr const & e) {
+        switch (e.kind()) {
+            case expr_kind::Var: return pp_var(e);
+            case expr_kind::Sort: return pp_sort(e);
+            case expr_kind::Constant: return pp_const(e);
+            case expr_kind::Meta: return pp_meta(e);
+            case expr_kind::Local: return pp_local(e);
+            case expr_kind::App: return pp_app(e);
+            case expr_kind::Lambda: return pp_lambda(e);
+            case expr_kind::Pi: return pp_pi(e);
+            case expr_kind::Macro: return pp_macro(e);
+            case expr_kind::Let: return pp_let(e);
+        }
+        lean_unreachable();
+    }
+};
+
+format simple_pp(name const & n) {
+    return pp_name(n);
+}
+
+format simple_pp(environment const & env, expr const & e) {
+    simple_pp_fn fn(env);
+    fn.mark_used_const_names(e);
+    return fn.pp(e);
+}
+
+}
diff --git a/src/checker/simple_pp.h b/src/checker/simple_pp.h
new file mode 100644
index 0000000000..9c6f29bdf9
--- /dev/null
+++ b/src/checker/simple_pp.h
@@ -0,0 +1,17 @@
+/*
+Copyright (c) 2017 Microsoft Corporation. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+
+Author: Gabriel Ebner
+*/
+#pragma once
+#include "kernel/environment.h"
+
+namespace lean {
+
+format compose_many(std::initializer_list<format> const & fmts);
+
+format simple_pp(name const & n);
+format simple_pp(environment const & env, expr const & e);
+
+}
diff --git a/src/cmake/run_checker.sh b/src/cmake/run_checker.sh
index 07b85bd604..98c5bbf1df 100644
--- a/src/cmake/run_checker.sh
+++ b/src/cmake/run_checker.sh
@@ -10,4 +10,4 @@ set -ex
 cd "$LEAN_PATH"
 # We pass "$LEAN_PATH" as a last argument here, because we don't have lrealpath on emscripten
 $emulator "$lean_bin" --recursive --export="$export_file" "$LEAN_PATH"
-$emulator "$leanchecker_bin" "$export_file"
+$emulator "$leanchecker_bin" "$export_file" nat.add_assoc