code: def is_decreasing(expression, interval=S.Reals, symbol=None):
      """
      Return whether the function is decreasing in the given interval.
  
      Parameters
      ==========
  
      expression : Expr
          The target function which is being checked.
      interval : Set, optional
          The range of values in which we are testing (defaults to set of
          all real numbers).
      symbol : Symbol, optional
          The symbol present in expression which gets varied over the given range.
  
      Returns
      =======
  
      Boolean
          True if ``expression`` is decreasing (either strictly decreasing or
          constant) in the given ``interval``, False otherwise.
  
      Examples
      ========
  
      >>> from sympy import is_decreasing
      >>> from sympy.abc import x, y
      >>> from sympy import S, Interval, oo
      >>> is_decreasing(1/(x**2 - 3*x), Interval.open(S(3)/2, 3))
      True
      >>> is_decreasing(1/(x**2 - 3*x), Interval.open(1.5, 3))
      True
      >>> is_decreasing(1/(x**2 - 3*x), Interval.Lopen(3, oo))
      True
      >>> is_decreasing(1/(x**2 - 3*x), Interval.Ropen(-oo, S(3)/2))
      False
      >>> is_decreasing(1/(x**2 - 3*x), Interval.Ropen(-oo, 1.5))
      False
      >>> is_decreasing(-x**2, Interval(-oo, 0))
      False
      >>> is_decreasing(-x**2 + y, Interval(-oo, 0), x)
      False
  
      """
      return monotonicity_helper(
          expression, lambda x: x <= 0, interval, symbol
      )
  
file_path: sympy/sympy/calculus/singularities.py
imports: from sympy.core.power import Pow
  from sympy.core.singleton import S
  from sympy.core.symbol import Symbol
  from sympy.core.sympify import sympify
  from sympy.functions.elementary.exponential import log
  from sympy.functions.elementary.trigonometric import sec, csc, cot, tan, cos
  from sympy.functions.elementary.hyperbolic import sech, csch, coth, tanh, cosh, asech, acsch, atanh, acoth
  from sympy.utilities.misc import filldedent
label_desc: Use image node_id 5 for calling a global function with example usage: is_decreasing(expression, interval, symbol) and returns: monotonicity_helper