class_docstr: A product of matrix expressions
  
  Examples
  ========
  
  >>> from sympy import MatMul, MatrixSymbol
  >>> A = MatrixSymbol('A', 5, 4)
  >>> B = MatrixSymbol('B', 4, 3)
  >>> C = MatrixSymbol('C', 3, 6)
  >>> MatMul(A, B, C)
  A*B*C
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code: def _eval_trace(self):
      factor, mmul = self.as_coeff_mmul()
      if factor != 1:
          from .trace import trace
  
          return factor * trace(mmul.doit())
  
imports: from sympy.assumptions.ask import ask, Q
  from sympy.assumptions.refine import handlers_dict
  from sympy.core import Basic, sympify, S
  from sympy.core.mul import mul, Mul
  from sympy.core.numbers import Number, Integer
  from sympy.core.symbol import Dummy
  from sympy.functions import adjoint
  from sympy.strategies import rm_id, unpack, typed, flatten, exhaust, do_one, new
  from sympy.matrices.exceptions import NonInvertibleMatrixError
  from sympy.matrices.matrixbase import MatrixBase
  from sympy.utilities.exceptions import sympy_deprecation_warning
  from sympy.matrices.expressions._shape import validate_matmul_integer
  from .inverse import Inverse
  from .matexpr import MatrixExpr
  from .matpow import MatPow
  from .transpose import transpose
  from .permutation import PermutationMatrix
  from .special import ZeroMatrix, Identity, GenericIdentity, OneMatrix
label_desc: Use image node_id 10 for calling the MatMul obj's underlying member method code with example usage: obj._eval_trace() and returns: unknown