diff --git a/src/builtin/obj/sum.olean b/src/builtin/obj/sum.olean
index c8d422d1fb..d40e91c110 100644
Binary files a/src/builtin/obj/sum.olean and b/src/builtin/obj/sum.olean differ
diff --git a/src/builtin/sum.lean b/src/builtin/sum.lean
index 3c98b0436f..5e01be3dca 100644
--- a/src/builtin/sum.lean
+++ b/src/builtin/sum.lean
@@ -68,7 +68,7 @@ theorem inr_inj {A B : (Type U)} {b1 b2 : B} : inr A b1 = inr A b2 → b1 = b2
      show b1 = b2,
         from optional::injectivity
             (calc some b1 = proj2 (pair (@none A) (some b1))  : refl (some b1)
-                      ... = proj2 (pair (@none A) (some b2))  : @proj2_congr _ _ (pair (@none A) (some b1)) (pair (@none A) (some b2)) rep_eq
+                      ... = proj2 (pair (@none A) (some b2))  : proj2_congr rep_eq
                       ... = some b2                           : refl (some b2))
 
 theorem distinct {A B : (Type U)} (a : A) (b : B) : inl a B ≠ inr A b
diff --git a/src/frontends/lean/frontend_elaborator.cpp b/src/frontends/lean/frontend_elaborator.cpp
index 5ed76cb7ca..abde407405 100644
--- a/src/frontends/lean/frontend_elaborator.cpp
+++ b/src/frontends/lean/frontend_elaborator.cpp
@@ -41,6 +41,7 @@ struct choice_value : public value {
     virtual expr get_type() const { lean_unreachable(); } // LCOV_EXCL_LINE
     virtual void write(serializer & ) const { lean_unreachable(); } // LCOV_EXCL_LINE
     virtual name get_name() const { return name("Choice"); }
+    virtual bool is_atomic_pp(bool /* unicode */, bool /* coercion */) const { return false; } // NOLINT
     virtual void display(std::ostream & out) const {
         out << "(Choice";
         for (auto c : m_choices) {
diff --git a/src/frontends/lean/pp.cpp b/src/frontends/lean/pp.cpp
index 3ee879ba56..c29d1b2cc2 100644
--- a/src/frontends/lean/pp.cpp
+++ b/src/frontends/lean/pp.cpp
@@ -262,7 +262,7 @@ class pp_fn {
         case expr_kind::Var: case expr_kind::Constant: case expr_kind::Type:
             return true;
         case expr_kind::Value:
-            return !is_choice(e);
+            return to_value(e).is_atomic_pp(m_unicode, m_coercion);
         case expr_kind::MetaVar:
             return !metavar_lctx(e);
         case expr_kind::App:
diff --git a/src/kernel/expr.h b/src/kernel/expr.h
index fc1350661c..c229af2043 100644
--- a/src/kernel/expr.h
+++ b/src/kernel/expr.h
@@ -331,6 +331,7 @@ public:
     virtual void display(std::ostream & out) const;
     virtual format pp() const;
     virtual format pp(bool unicode, bool coercion) const;
+    virtual bool is_atomic_pp(bool unicode, bool coercion) const = 0;
     virtual int push_lua(lua_State * L) const;
     virtual unsigned hash() const;
     virtual void write(serializer & s) const = 0;
diff --git a/src/kernel/normalizer.cpp b/src/kernel/normalizer.cpp
index d556d0e2a9..20f42d7659 100644
--- a/src/kernel/normalizer.cpp
+++ b/src/kernel/normalizer.cpp
@@ -67,6 +67,7 @@ public:
     expr const & get_expr() const { return m_expr; }
     context const & get_context() const { return m_ctx; }
     value_stack const & get_stack() const { return m_stack; }
+    virtual bool is_atomic_pp(bool /* unicode */, bool /* coercion */) const { return false; } // NOLINT
 };
 
 expr mk_closure(expr const & e, context const & ctx, value_stack const & s) { return mk_value(*(new closure(e, ctx, s))); }
diff --git a/src/kernel/value.h b/src/kernel/value.h
index 0ad7336a1f..bb0e43b484 100644
--- a/src/kernel/value.h
+++ b/src/kernel/value.h
@@ -17,6 +17,7 @@ public:
     named_value(name const & n):m_name(n) {}
     virtual ~named_value() {}
     virtual name get_name() const { return m_name; }
+    virtual bool is_atomic_pp(bool /* unicode */, bool /* coercion */) const { return true; } // NOLINT
 };
 
 /**
diff --git a/src/library/arith/int.cpp b/src/library/arith/int.cpp
index 9393700590..2f3f98b466 100644
--- a/src/library/arith/int.cpp
+++ b/src/library/arith/int.cpp
@@ -44,6 +44,7 @@ public:
         else
             return format(m_val);
     }
+    virtual bool is_atomic_pp(bool /* unicode */, bool coercion) const { return !coercion || m_val < 0; }
     virtual unsigned hash() const { return m_val.hash(); }
     virtual int push_lua(lua_State * L) const { return push_mpz(L, m_val); }
     mpz const & get_num() const { return m_val; }
diff --git a/src/library/arith/nat.cpp b/src/library/arith/nat.cpp
index 37f611e691..ec575c4181 100644
--- a/src/library/arith/nat.cpp
+++ b/src/library/arith/nat.cpp
@@ -36,6 +36,7 @@ public:
     virtual void display(std::ostream & out) const { out << m_val; }
     virtual format pp() const { return format(m_val); }
     virtual format pp(bool, bool) const { return pp(); }
+    virtual bool is_atomic_pp(bool /* unicode */, bool /* coercion */) const { return true; } // NOLINT
     virtual unsigned hash() const { return m_val.hash(); }
     virtual int push_lua(lua_State * L) const { return push_mpz(L, m_val); }
     mpz const & get_num() const { return m_val; }
diff --git a/src/library/arith/real.cpp b/src/library/arith/real.cpp
index ed8a8a5fbf..0ff87f0e2d 100644
--- a/src/library/arith/real.cpp
+++ b/src/library/arith/real.cpp
@@ -48,6 +48,7 @@ public:
         else
             return format(m_val);
     }
+    virtual bool is_atomic_pp(bool /* unicode */, bool coercion) const { return !coercion; }
     virtual unsigned hash() const { return m_val.hash(); }
     virtual int push_lua(lua_State * L) const { return push_mpq(L, m_val); }
     mpq const & get_num() const { return m_val; }
diff --git a/src/library/elaborator/elaborator.cpp b/src/library/elaborator/elaborator.cpp
index 032a4e36bf..dc3a75633b 100644
--- a/src/library/elaborator/elaborator.cpp
+++ b/src/library/elaborator/elaborator.cpp
@@ -538,11 +538,6 @@ class elaborator::imp {
                             swap(new_a, new_b);
                         push_new_constraint(is_eq(c), *new_ctx, new_a, new_b, new_jst);
                         return Processed;
-                    } else if (!has_metavar(b)) {
-                        // Failure, there is no way to unify
-                        // ?m[lift:s:n, ...] with a term that contains variables in [s, s+n]
-                        m_conflict = mk_failure_justification(c);
-                        return Failed;
                     }
                 }
             }
@@ -562,6 +557,28 @@ class elaborator::imp {
         return Continue;
     }
 
+    bool check_metavar_lift(unification_constraint const & c, expr const & a, expr const & b) {
+        if (is_metavar(a) && has_local_context(a) && !has_metavar(b)) {
+            lean_assert(!is_assigned(a));
+            local_entry const & me = head(metavar_lctx(a));
+            if (me.is_lift()) {
+                // a is of the form ?m[lift:s:n]
+                unsigned s = me.s();
+                unsigned n = me.n();
+                if (has_free_var(b, s, s + n, m_state.m_menv)) {
+                    // Failure, there is no way to unify
+                    // ?m[lift:s:n, ...] with a term that contains variables in [s, s+n]
+
+                    // In older commits, this check was being done inside of process_metavar.
+                    // This was incorrect. This check must be performed AFTER b is normalized.
+                    m_conflict = mk_failure_justification(c);
+                    return false;
+                }
+            }
+        }
+        return true;
+    }
+
     justification mk_subst_justification(unification_constraint const & c, buffer<justification> const & subst_justifications) {
         if (subst_justifications.size() == 1) {
             return justification(new substitution_justification(c, subst_justifications[0]));
@@ -729,6 +746,8 @@ class elaborator::imp {
             expr new_a = normalize_step(ctx, a);
             expr new_b = normalize_step(ctx, b);
             if (new_a == a && new_b == b) {
+                if (is_meta(a) || is_meta(b))
+                    break; // we do not unfold if one of the arguments is a metavar or metavar_app
                 int w_a = get_unfolding_weight(a);
                 int w_b = get_unfolding_weight(b);
                 if (w_a >= 0 || w_b >= 0) {
@@ -1687,7 +1706,9 @@ class elaborator::imp {
             }
         }
 
-        if (!is_meta(a) && !is_meta(b) && normalize_head(a, b, c)) { return true; }
+        if (!is_meta_app(a) && !is_meta_app(b) && normalize_head(a, b, c)) { return true; }
+
+        if (!check_metavar_lift(c, a, b) || !check_metavar_lift(c, b, a)) { return false; }
 
         if (process_simple_ho_match(ctx, a, b, true, c) ||
             process_simple_ho_match(ctx, b, a, false, c))