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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def let_statement(u):
 """ If LHS is a plain variable, and RHS is a matrix enclosed in square brackets, replace the matrix expr with a funcall. """

    if u.__class__ is node.let:
        if (u.ret.__class__ is node.ident and
            u.args.__class__ is node.matrix):
            u.args = node.funcall(func_expr=node.ident("matlabarray"),
                                  args=node.expr_list([u.args]))