'Lower triangular matrix predicate.
A matrix ``M`` is called lower triangular matrix if :math:`a_{ij}=0`
for :math:`i>j`.
Examples
>>> from sympy import Q, ask, ZeroMatrix, Identity
>>> ask(Q.lower_triangular(Identity(3)))
True
>>> ask(Q.lower_triangular(ZeroMatrix(3, 3)))
True
References
.. [1] http://mathworld.wolfram.com/LowerTriangularMatrix.html'

@predicate_memo
def lower_triangular(self):

    return Predicate('lower_triangular')
