He ruled on this issue and cited support from our Gemora. It was taught in a braisa: A metzora whose eighth day (of purification) fell on Erev Pesach, but on that day had an emission of semen (resulting in the fact that he now cannot enter the Temple Mount to complete his purification process), and then immersed himself, the Chachamim said that although an ordinary tevul yom (one who has immersed in a mikvah but still has tumah on him until nightfall) may not enter the Temple Mount until nightfall, this one may enter in order to complete his purification process, thus enabling him to bring his pesach offering. It is preferable for a positive commandment that involves kares (pesach obligation) to override a positive commandment that does not involve kares (entering the Temple Mount while being a tevul yom).
Rabbi Yochanan maintains that it is only Rabbinically forbidden for a tevul yom to enter the Temple Mount.
Ula said: Why do we allow this tevul yom to enter? He answers: Since we would allow an ordinary metzora to enter the Temple Mount in order to complete his purification process, we allow a metzora who has had an emission of semen to enter as well.
Tosfos asks: Ula maintains that a partial entry into an area which is forbidden to enter is regarded as a full entry. If so, why do we limit this metzora, who is a tevul yom to insert his right ear, thumb and big toe into the Temple Courtyard, let him be permitted to enter entirely? What would be the distinction?
Tosfos answers: Entering completely into the Courtyard is regarded as being more severe than a partial entry. The Torah forbids a tevul yom from entering completely into the Courtyard explicitly, but a partial entry is only derived through the means of a hekesh (a Midrashic juxtaposition). Although both prohibitions are Biblical, the one that is written explicitly is stricter than the one which is merely derived from an exposition.
It emerges from here that a Biblical prohibition written explicitly is more stringent than one which is only derived through an exposition. He therefore posits that it would be preferable to engage in the labor which would only be violating a toldah rather than one which would constitute an av melocha. This is because a toldah is not written explicitly in the Torah.