The Ran holds that the concept of requiring opposites for bitul is d'oraysa, but on a d'oraysa level even a davar sheyesh lo matirin is assur enough to be opposite of heter and is batul in the heter. What would be the din of a davar sheyesh lo matirin that falls into a davar sheyesh lo matirin where the issur on the former will expire after the issur on the latter? For example if someone makes a 30 day neder on something that gets mixed up with something else that is assur to him b'neder and will expire in 10 days. Do we say that since at the time of the ta'aroves bitul cannot take place (i am assuming that this is even d'oraysa) because the heter and the issur are too similar, so even when the 10 days expire the ta'aroves will remain assur d'oraysa, or do we say that when the 10 days are up there is bitul d'oraysa since it becomes a standard case of davar sheyesh lo matririn so there is bitul d'oraysa just not d'rabonon? Furthermore, within the 10 days if one would eat the mixture it would seem to be a d'oraysa violation of both nedarim because the 30 day issur cannot be batul in the 10 day issur since right now they are too similar to facilitate bitul. - food for thought!