diff --git a/diofant/calculus/order.py b/diofant/calculus/order.py
index 812d5ec1a4a..389fb0c5baf 100644
--- a/diofant/calculus/order.py
+++ b/diofant/calculus/order.py
@@ -2,7 +2,6 @@
                     expand_log, expand_power_base, nan, oo, sympify)
 from ..core.compatibility import is_sequence
 from ..utilities import default_sort_key
-from ..utilities.iterables import uniq
 
 
 class Order(Expr):
@@ -72,13 +71,6 @@ class Order(Expr):
     >>> O(cos(x), (x, pi/2))
     O(x - pi/2, (x, pi/2))
 
-    >>> O(1 + x*y)
-    O(1, x, y)
-    >>> O(1 + x*y, (x, 0), (y, 0))
-    O(1, x, y)
-    >>> O(1 + x*y, (x, oo), (y, oo))
-    O(x*y, (x, oo), (y, oo))
-
     References
     ==========
 
@@ -111,12 +103,12 @@ def __new__(cls, expr, *args, **kwargs):
                 variables = list(map(sympify, args))
                 point = [Integer(0)]*len(variables)
 
+        if len(variables) > 1:
+            raise TypeError
+
         if not all(isinstance(v, (Dummy, Symbol)) for v in variables):
             raise TypeError(f'Variables are not symbols, got {variables}')
 
-        if len(list(uniq(variables))) != len(variables):
-            raise ValueError(f'Variables are supposed to be unique symbols, got {variables}')
-
         if expr.is_Order:
             expr_vp = dict(expr.args[1:])
             new_vp = dict(expr_vp)
@@ -163,14 +155,6 @@ def __new__(cls, expr, *args, **kwargs):
             else:
                 args = tuple(variables)
 
-            if len(variables) > 1:
-                # XXX: better way?  We need this expand() to
-                # workaround e.g: expr = x*(x + y).
-                # (x*(x + y)).as_leading_term(x, y) currently returns
-                # x*y (wrong order term!).  That's why we want to deal with
-                # expand()'ed expr (handled in "if expr.is_Add" branch below).
-                expr = expr.expand()
-
             if expr.is_Add:
                 lst = expr.extract_leading_order(args)
                 expr = Add(*[f.expr for (e, f) in lst])
@@ -182,42 +166,38 @@ def __new__(cls, expr, *args, **kwargs):
                 expr = expand_power_base(expr)
                 expr = expand_log(expr)
 
-                if len(args) == 1:
-                    # The definition of O(f(x)) symbol explicitly stated that
-                    # the argument of f(x) is irrelevant.  That's why we can
-                    # combine some power exponents (only "on top" of the
-                    # expression tree for f(x)), e.g.:
-                    # x**p * (-x)**q -> x**(p+q) for real p, q.
-                    x = args[0]
-                    margs = list(Mul.make_args(
-                        expr.as_independent(x, as_Add=False)[1]))
-
-                    for i, t in enumerate(margs):
-                        if t.is_Pow:
-                            b, q = t.base, t.exp
-                            if b in (x, -x) and q.is_extended_real and not q.has(x):
-                                margs[i] = x**q
-                            elif b.is_Pow and not b.exp.has(x):
+                # The definition of O(f(x)) symbol explicitly stated that
+                # the argument of f(x) is irrelevant.  That's why we can
+                # combine some power exponents (only "on top" of the
+                # expression tree for f(x)), e.g.:
+                # x**p * (-x)**q -> x**(p+q) for real p, q.
+                x = args[0]
+                margs = list(Mul.make_args(
+                    expr.as_independent(x, as_Add=False)[1]))
+
+                for i, t in enumerate(margs):
+                    if t.is_Pow:
+                        b, q = t.base, t.exp
+                        if b in (x, -x) and q.is_extended_real and not q.has(x):
+                            margs[i] = x**q
+                        elif b.is_Pow and not b.exp.has(x):
+                            b, r = b.base, b.exp
+                            if b in (x, -x) and r.is_extended_real:
+                                margs[i] = x**(r*q)
+                        elif b.is_Mul and b.args[0] == -1:
+                            b = -b
+                            if b.is_Pow and not b.exp.has(x):
                                 b, r = b.base, b.exp
                                 if b in (x, -x) and r.is_extended_real:
                                     margs[i] = x**(r*q)
-                            elif b.is_Mul and b.args[0] == -1:
-                                b = -b
-                                if b.is_Pow and not b.exp.has(x):
-                                    b, r = b.base, b.exp
-                                    if b in (x, -x) and r.is_extended_real:
-                                        margs[i] = x**(r*q)
 
-                    expr = Mul(*margs)
+                expr = Mul(*margs)
 
             expr = expr.subs(rs)
 
         if expr == 0:
             return expr
 
-        if expr.is_Order:
-            expr = expr.expr
-
         if not expr.has(*variables):
             expr = Integer(1)
 
@@ -321,9 +301,6 @@ def contains(self, expr):
                 return all(x in self.args[1:] for x in expr.args[1:])
             if expr.expr.is_Add:
                 return all(self.contains(x) for x in expr.expr.args)
-            if self.expr.is_Add and point == 0:
-                return any(self.func(x, *self.args[1:]).contains(expr)
-                           for x in self.expr.args)
             if self.variables and expr.variables:
                 common_symbols = tuple(s for s in self.variables if s in expr.variables)
             elif self.variables:
@@ -332,7 +309,6 @@ def contains(self, expr):
                 common_symbols = expr.variables
             if not common_symbols:
                 return
-            r = None
             ratio = self.expr/expr.expr
             ratio = powsimp(ratio, deep=True, combine='exp')
             for s in common_symbols:
@@ -341,12 +317,7 @@ def contains(self, expr):
                     l = l != 0
                 else:
                     l = None
-                if r is None:
-                    r = l
-                else:
-                    if r != l:
-                        return
-            return r
+            return l
         obj = self.func(expr, *self.args[1:])
         return self.contains(obj)
 
diff --git a/diofant/core/expr.py b/diofant/core/expr.py
index 97537021009..118a5850981 100644
--- a/diofant/core/expr.py
+++ b/diofant/core/expr.py
@@ -2702,7 +2702,7 @@ def compute_leading_term(self, x, logx=None):
         return t.as_leading_term(x)
 
     @cacheit
-    def as_leading_term(self, *symbols):
+    def as_leading_term(self, x):
         """Returns the leading (nonzero) term of the series expansion of self.
 
         The _eval_as_leading_term routines are used to do this, and they must
@@ -2718,14 +2718,7 @@ def as_leading_term(self, *symbols):
 
         """
         from ..simplify import powsimp
-        if len(symbols) > 1:
-            c = self
-            for x in symbols:
-                c = c.as_leading_term(x)
-            return c
-        if not symbols:
-            return self
-        x = sympify(symbols[0])
+        x = sympify(x)
         if not x.is_Symbol:
             raise ValueError(f'expecting a Symbol but got {x}')
         if x not in self.free_symbols:
diff --git a/diofant/printing/latex.py b/diofant/printing/latex.py
index 685ce840036..7d5435bca9c 100644
--- a/diofant/printing/latex.py
+++ b/diofant/printing/latex.py
@@ -1105,18 +1105,11 @@ def _print_Rational(self, expr):
 
     def _print_Order(self, expr):
         s = self._print(expr.expr)
-        if expr.point and any(p != 0 for p in expr.point) or \
-           len(expr.variables) > 1:
+        if expr.point and any(p != 0 for p in expr.point):
             s += '; '
-            if len(expr.variables) > 1:
-                s += self._print(expr.variables)
-            else:
-                s += self._print(expr.variables[0])
+            s += self._print(expr.variables[0])
             s += r'\rightarrow{}'
-            if len(expr.point) > 1:
-                s += self._print(expr.point)
-            else:
-                s += self._print(expr.point[0])
+            s += self._print(expr.point[0])
         return r'\mathcal{O}\left(%s\right)' % s
 
     def _print_Symbol(self, expr):
diff --git a/diofant/printing/pretty/pretty.py b/diofant/printing/pretty/pretty.py
index 94cad6e09e2..1de9f4e0050 100644
--- a/diofant/printing/pretty/pretty.py
+++ b/diofant/printing/pretty/pretty.py
@@ -935,21 +935,14 @@ def _print_Lambda(self, e):
 
     def _print_Order(self, expr):
         pform = self._print(expr.expr)
-        if ((expr.point and any(p != 0 for p in expr.point)) or
-                len(expr.variables) > 1):
+        if expr.point and any(p != 0 for p in expr.point):
             pform = prettyForm(*pform.right('; '))
-            if len(expr.variables) > 1:
-                pform = prettyForm(*pform.right(self._print(expr.variables)))
-            else:
-                pform = prettyForm(*pform.right(self._print(expr.variables[0])))
+            pform = prettyForm(*pform.right(self._print(expr.variables[0])))
             if self._use_unicode:
                 pform = prettyForm(*pform.right(' \N{RIGHTWARDS ARROW} '))
             else:
                 pform = prettyForm(*pform.right(' -> '))
-            if len(expr.point) > 1:
-                pform = prettyForm(*pform.right(self._print(expr.point)))
-            else:
-                pform = prettyForm(*pform.right(self._print(expr.point[0])))
+            pform = prettyForm(*pform.right(self._print(expr.point[0])))
         pform = prettyForm(*pform.parens())
         pform = prettyForm(*pform.left('O'))
         return pform
diff --git a/diofant/printing/str.py b/diofant/printing/str.py
index d6ca593a819..cdb763a3c43 100644
--- a/diofant/printing/str.py
+++ b/diofant/printing/str.py
@@ -273,9 +273,7 @@ def _print_NegativeInfinity(self, expr):
 
     def _print_Order(self, expr):
         if all(p == 0 for p in expr.point) or not expr.variables:
-            if len(expr.variables) <= 1:
-                return f'O({self._print(expr.expr)})'
-            return f"O({self.stringify((expr.expr,) + expr.variables, ', ', 0)})"
+            return f'O({self._print(expr.expr)})'
         return f"O({self.stringify(expr.args, ', ', 0)})"
 
     def _print_Cycle(self, expr):
diff --git a/diofant/tests/calculus/test_order.py b/diofant/tests/calculus/test_order.py
index 864ffe1031e..47432a46571 100644
--- a/diofant/tests/calculus/test_order.py
+++ b/diofant/tests/calculus/test_order.py
@@ -2,8 +2,7 @@
 
 from diofant import (Add, Derivative, Function, I, Integer, Integral, O,
                      Rational, Symbol, conjugate, cos, digamma, exp, expand,
-                     factorial, ln, log, nan, oo, pi, sin, sqrt, symbols,
-                     transpose)
+                     factorial, ln, log, nan, oo, pi, sin, sqrt, transpose)
 from diofant.abc import w, x, y, z
 
 
@@ -22,8 +21,6 @@ def test_free_symbols():
     assert O(1).free_symbols == set()
     assert O(x).free_symbols == {x}
     assert O(1, x).free_symbols == {x}
-    assert O(x*y).free_symbols == {x, y}
-    assert O(x, x, y).free_symbols == {x, y}
 
 
 def test_simple_1():
@@ -32,7 +29,6 @@ def test_simple_1():
     assert O(x)*3 == O(x)
     assert -28*O(x) == O(x)
     assert O(O(x)) == O(x)
-    assert O(O(x), y) == O(O(x), x, y)
     assert O(-23) == O(1)
     assert O(exp(x)) == O(1, x)
     assert O(exp(1/x)).expr == exp(1/x)
@@ -41,7 +37,6 @@ def test_simple_1():
     assert O(x**(5*o/3)).expr == x**(5*o/3)
     assert O(x**2 + x + y, x) == O(1, x)
     assert O(x**2 + x + y, y) == O(1, y)
-    pytest.raises(ValueError, lambda: O(exp(x), x, x))
     pytest.raises(TypeError, lambda: O(x, 2 - x))
     pytest.raises(ValueError, lambda: O(x, (x, x**2)))
 
@@ -131,13 +126,6 @@ def test_contains():
     assert not O(exp(1/x)).contains(O(exp(2/x)))
 
     assert O(x).contains(O(y)) is None
-    assert O(x).contains(O(y*x))
-    assert O(y*x).contains(O(x))
-    assert O(y).contains(O(x*y))
-    assert O(x).contains(O(y**2*x))
-
-    assert O(x*y**2).contains(O(x**2*y)) is None
-    assert O(x**2*y).contains(O(x*y**2)) is None
 
     assert O(sin(1/x**2)).contains(O(cos(1/x**2))) is None
     assert O(cos(1/x**2)).contains(O(sin(1/x**2))) is None
@@ -149,6 +137,7 @@ def test_contains():
     assert O(1, x) not in O(1)
     assert O(1) in O(1, x)
     pytest.raises(TypeError, lambda: O(x*y**2) in O(x**2*y))
+    pytest.raises(TypeError, lambda: O(x**y, x) in O(x**z, x))
 
 
 def test_add_1():
@@ -164,50 +153,6 @@ def test_add_1():
 def test_ln_args():
     assert O(log(x)) + O(log(2*x)) == O(log(x))
     assert O(log(x)) + O(log(x**3)) == O(log(x))
-    assert O(log(x*y)) + O(log(x) + log(y)) == O(log(x*y))
-
-
-def test_multivar_0():
-    assert O(x*y).expr == x*y
-    assert O(x*y**2).expr == x*y**2
-    assert O(x*y, x).expr == x
-    assert O(x*y**2, y).expr == y**2
-    assert O(x*y*z).expr == x*y*z
-    assert O(x/y).expr == x/y
-    assert O(x*exp(1/y)).expr == x*exp(1/y)
-    assert O(exp(x)*exp(1/y)).expr == exp(1/y)
-
-
-def test_multivar_0a():
-    assert O(exp(1/x)*exp(1/y)).expr == exp(1/x + 1/y)
-
-
-def test_multivar_1():
-    assert O(x + y).expr == x + y
-    assert O(x + 2*y).expr == x + y
-    assert (O(x + y) + x).expr == (x + y)
-    assert (O(x + y) + x**2) == O(x + y)
-    assert (O(x + y) + 1/x) == 1/x + O(x + y)
-    assert O(x**2 + y*x).expr == x**2 + y*x
-
-
-def test_multivar_2():
-    assert O(x**2*y + y**2*x, x, y).expr == x**2*y + y**2*x
-
-
-def test_multivar_mul_1():
-    assert O(x + y)*x == O(x**2 + y*x, x, y)
-
-
-def test_multivar_3():
-    assert (O(x) + O(y)).args in [
-        (O(x), O(y)),
-        (O(y), O(x))]
-    assert O(x) + O(y) + O(x + y) == O(x + y)
-    assert (O(x**2*y) + O(y**2*x)).args in [
-        (O(x*y**2), O(y*x**2)),
-        (O(y*x**2), O(x*y**2))]
-    assert (O(x**2*y) + O(y*x)) == O(x*y)
 
 
 def test_sympyissue_3468():
@@ -246,7 +191,6 @@ def test_order_leadterm():
 
 def test_order_symbols():
     e = x*y*sin(x)*Integral(x, (x, 1, 2))
-    assert O(e) == O(x**2*y)
     assert O(e, x) == O(x**2)
 
 
@@ -302,16 +246,6 @@ def test_eval():
     assert (O(1)**x).is_Pow
 
 
-def test_sympyissue_4279():
-    a, b = symbols('a b')
-    assert O(a, a, b) + O(1, a, b) == O(1, a, b)
-    assert O(b, a, b) + O(1, a, b) == O(1, a, b)
-    assert O(a + b) + O(1, a, b) == O(1, a, b)
-    assert O(1, a, b) + O(a, a, b) == O(1, a, b)
-    assert O(1, a, b) + O(b, a, b) == O(1, a, b)
-    assert O(1, a, b) + O(a + b) == O(1, a, b)
-
-
 def test_sympyissue_4855():
     assert 1/O(1) != O(1)
     assert 1/O(x) != O(1/x)
@@ -359,8 +293,6 @@ def test_order_at_infinity():
     assert O(3*x, (x, oo)) == O(x, (x, oo))
     assert O(x, (x, oo))*3 == O(x, (x, oo))
     assert -28*O(x, (x, oo)) == O(x, (x, oo))
-    assert O(O(x, (x, oo)), (x, oo)) == O(x, (x, oo))
-    assert O(O(x, (x, oo)), (y, oo)) == O(x, (x, oo), (y, oo))
     assert O(3, (x, oo)) == O(1, (x, oo))
     assert O(x**2 + x + y, (x, oo)) == O(x**2, (x, oo))
     assert O(x**2 + x + y, (y, oo)) == O(y, (y, oo))
@@ -432,8 +364,6 @@ def test_order_subs_limits():
     assert O(x**2).subs({x: y - 1}) == O((y - 1)**2, (y, 1))
     assert O(10*x**2, (x, 2)).subs({x: y - 1}) == O(1, (y, 3))
 
-    assert O(x).subs({x: y*z}) == O(y*z, y, z)
-
     assert O(1/x, (x, oo)).subs({x: +I*x}) == O(1/x, (x, -I*oo))
     assert O(1/x, (x, oo)).subs({x: -I*x}) == O(1/x, (x, +I*oo))
 
diff --git a/diofant/tests/core/test_args.py b/diofant/tests/core/test_args.py
index 7d052735e9f..07c700c846b 100644
--- a/diofant/tests/core/test_args.py
+++ b/diofant/tests/core/test_args.py
@@ -1432,7 +1432,7 @@ def test_diofant__calculus__limits__Limit():
 
 
 def test_diofant__calculus__order__Order():
-    assert _test_args(Order(1, x, y))
+    assert _test_args(Order(1, x))
 
 
 def test_diofant__simplify__hyperexpand__Hyper_Function():
diff --git a/diofant/tests/functions/test_trigonometric.py b/diofant/tests/functions/test_trigonometric.py
index 8e126dbb35d..ff13f160a98 100644
--- a/diofant/tests/functions/test_trigonometric.py
+++ b/diofant/tests/functions/test_trigonometric.py
@@ -1302,8 +1302,6 @@ def test_sec():
     assert sec(a).is_algebraic is None
     assert sec(na).is_algebraic is False
 
-    assert sec(x).as_leading_term() == sec(x)
-
     assert sec(0).is_finite
     assert sec(x).is_finite is None
     assert sec(pi/2).is_finite is False
@@ -1376,8 +1374,6 @@ def test_csc():
     assert csc(a).is_algebraic is None
     assert csc(na).is_algebraic is False
 
-    assert csc(x).as_leading_term() == csc(x)
-
     assert csc(0).is_finite is False
     assert csc(x).is_finite is None
     assert csc(pi/2).is_finite
diff --git a/diofant/tests/printing/test_latex.py b/diofant/tests/printing/test_latex.py
index debccb2a90a..f6ee28740c3 100644
--- a/diofant/tests/printing/test_latex.py
+++ b/diofant/tests/printing/test_latex.py
@@ -333,9 +333,6 @@ def test_latex_functions():
     assert latex(Order(x, x)) == r'\mathcal{O}\left(x\right)'
     assert latex(Order(x, (x, 0))) == r'\mathcal{O}\left(x\right)'
     assert latex(Order(x, (x, oo))) == r'\mathcal{O}\left(x; x\rightarrow{}\infty\right)'
-    assert latex(Order(x, x, y)) == r'\mathcal{O}\left(x; \left ( x, \quad y\right )\rightarrow{}\left ( 0, \quad 0\right )\right)'
-    assert latex(Order(x, x, y)) == r'\mathcal{O}\left(x; \left ( x, \quad y\right )\rightarrow{}\left ( 0, \quad 0\right )\right)'
-    assert latex(Order(x, (x, oo), (y, oo))) == r'\mathcal{O}\left(x; \left ( x, \quad y\right )\rightarrow{}\left ( \infty, \quad \infty\right )\right)'
     assert latex(lowergamma(x, y)) == r'\gamma\left(x, y\right)'
     assert latex(lowergamma(x, y)**3) == r'\gamma^{3}\left(x, y\right)'
     assert latex(uppergamma(x, y)) == r'\Gamma\left(x, y\right)'
diff --git a/diofant/tests/printing/test_pretty.py b/diofant/tests/printing/test_pretty.py
index 25aea4da346..31182860111 100644
--- a/diofant/tests/printing/test_pretty.py
+++ b/diofant/tests/printing/test_pretty.py
@@ -193,7 +193,6 @@
 
 O(1)
 O(1/x)
-O(x**2 + y**2)
 """
 
 
@@ -2041,20 +2040,6 @@ def test_pretty_order():
     assert pretty(expr) == ascii_str
     assert upretty(expr) == ucode_str
 
-    expr = O(x**2 + y**2)
-    ascii_str = \
-        """\
- / 2    2                  \\\n\
-O\\x  + y ; (x, y) -> (0, 0)/\
-"""
-    ucode_str = \
-        """\
- ⎛ 2    2                 ⎞\n\
-O⎝x  + y ; (x, y) → (0, 0)⎠\
-"""
-    assert pretty(expr) == ascii_str
-    assert upretty(expr) == ucode_str
-
     expr = O(1, (x, oo))
     ascii_str = \
         """\
@@ -2083,20 +2068,6 @@ def test_pretty_order():
     assert pretty(expr) == ascii_str
     assert upretty(expr) == ucode_str
 
-    expr = O(x**2 + y**2, (x, oo), (y, oo))
-    ascii_str = \
-        """\
- / 2    2                    \\\n\
-O\\x  + y ; (x, y) -> (oo, oo)/\
-"""
-    ucode_str = \
-        """\
- ⎛ 2    2                 ⎞\n\
-O⎝x  + y ; (x, y) → (∞, ∞)⎠\
-"""
-    assert pretty(expr) == ascii_str
-    assert upretty(expr) == ucode_str
-
 
 def test_pretty_derivatives():
     # Simple
diff --git a/diofant/tests/printing/test_str.py b/diofant/tests/printing/test_str.py
index 3fa52509468..a97ee3d1c7f 100644
--- a/diofant/tests/printing/test_str.py
+++ b/diofant/tests/printing/test_str.py
@@ -247,13 +247,9 @@ def test_NegativeInfinity():
 def test_Order():
     assert str(O(x)) == 'O(x)'
     assert str(O(x**2)) == 'O(x**2)'
-    assert str(O(x*y)) == 'O(x*y, x, y)'
     assert str(O(x, x)) == 'O(x)'
     assert str(O(x, (x, 0))) == 'O(x)'
     assert str(O(x, (x, oo))) == 'O(x, (x, oo))'
-    assert str(O(x, x, y)) == 'O(x, x, y)'
-    assert str(O(x, x, y)) == 'O(x, x, y)'
-    assert str(O(x, (x, oo), (y, oo))) == 'O(x, (x, oo), (y, oo))'
 
 
 def test_Permutation_Cycle():