code: def refine(expr, assumptions=True):
      """
      Simplify an expression using assumptions.
  
      Explanation
      ===========
  
      Unlike :func:`~.simplify()` which performs structural simplification
      without any assumption, this function transforms the expression into
      the form which is only valid under certain assumptions. Note that
      ``simplify()`` is generally not done in refining process.
  
      Refining boolean expression involves reducing it to ``S.true`` or
      ``S.false``. Unlike :func:`~.ask()`, the expression will not be reduced
      if the truth value cannot be determined.
  
      Examples
      ========
  
      >>> from sympy import refine, sqrt, Q
      >>> from sympy.abc import x
      >>> refine(sqrt(x**2), Q.real(x))
      Abs(x)
      >>> refine(sqrt(x**2), Q.positive(x))
      x
  
      >>> refine(Q.real(x), Q.positive(x))
      True
      >>> refine(Q.positive(x), Q.real(x))
      Q.positive(x)
  
      See Also
      ========
  
      sympy.simplify.simplify.simplify : Structural simplification without assumptions.
      sympy.assumptions.ask.ask : Query for boolean expressions using assumptions.
      """
      if not isinstance(expr, Basic):
          return expr
  
      if not expr.is_Atom:
          args = [refine(arg, assumptions) for arg in expr.args]
          # TODO: this will probably not work with Integral or Polynomial
          expr = expr.func(*args)
      if hasattr(expr, "_eval_refine"):
          ref_expr = expr._eval_refine(assumptions)
          if ref_expr is not None:
              return ref_expr
      name = expr.__class__.__name__
      handler = handlers_dict.get(name, None)
      if handler is None:
          return expr
      new_expr = handler(expr, assumptions)
      if (new_expr is None) or (expr == new_expr):
          return expr
      if not isinstance(new_expr, Expr):
          return new_expr
      return refine(new_expr, assumptions)
  
file_path: sympy/sympy/assumptions/refine.py
imports: from __future__ import annotations
  from typing import Callable
  from sympy.core import S, Add, Expr, Basic, Mul, Pow, Rational
  from sympy.core.logic import fuzzy_not
  from sympy.logic.boolalg import Boolean
  from sympy.assumptions import ask, Q
label_desc: Use image node_id 1 for calling a global function with example usage: refine(expr, assumptions) and returns: refine, expr, expr, expr, new_expr, ref_expr