@property
def evaluate(self):
    # Evaluate finite-difference.
    # Note: evaluate and _eval_fd splitted for potential future different
    # types of discretizations.
    do = self.deriv_order
    if isinstance(do,int): do = (do,)
    for i, d in enumerate(self.dims):
        expr_order = self.expr.time_order if d.is_Time else self.expr.space_order
        if do[i] > expr_order:
            raise ValueError("Expression order must be equal or greater than "
                             "Derivative order")
    return self._eval_fd(self.expr)

from devito import (Grid, TimeFunction, Eq, Operator)

grid = Grid(tuple([11]*2))

u = TimeFunction(name="u", grid=grid, space_order=2, time_order=2)
m = TimeFunction(name="m", grid=grid, space_order=1, time_order=1)

# op = Operator(Eq(u.forward,u.biharmonic(1/m)))
# op = Operator(Eq(u.forward,(u * m).dx2))
op = Operator(Eq(u.forward,(u * m).dt2))

op.apply(time=0)