Yield transfers obtained from result.

def _transfers(reaction, delta, elements, result, epsilon):
    """Yield transfers obtained from result."""
    left = set(c for c, _ in reaction.left)
    right = set(c for c, _ in reaction.right)
    for c1, c2 in product(left, right):
        items = {}
        for e in elements:
            v = result.get_value(delta[c1, c2, e])
            nearest_int = round(v)
            if abs(v - nearest_int) < epsilon:
                v = int(nearest_int)
            if v >= epsilon:
                items[e] = v

        if len(items) > 0:
            yield (c1, c2), Formula(items)