On Peninei Halakha halachot shabath about Hotza’ah it's written:
Many maintain that as long as one did not stop walking while in the reshut ha-rabim, the prohibition is only rabbinic, because as long as he is walking he has not performed a hanaĥa in the reshut ha-rabim (Rashba and Ritva, Eruvin 33a; Taz 346:2). Indeed, practical halakha follows this position (SAH 347:9; R. Shlomo Zalman Auerbach cited in SSK ch. 30 n. 134). Therefore, where there is uncertainty about the validity of the local eruv, one may carry while walking nonstop from a reshut ha-yaĥid to another reshut ha-yaĥid via a reshut ha-rabim.
But further on, it's written:
We have seen in the previous sections that the prohibition of Hotza’ah includes transporting an object more than four amot in a public domain, since one’s personal space within the public domain is defined as four amot. If he transports an object further, he is deemed to have moved it to a different domain and transgressed Torah law. But within a square of four amot by four amot one may carry. Therefore, only one who carries something a distance greater than the diagonal of a four-amot square (2.58 m) has violated a Torah prohibition, because only then is it clear that he carried outside the permissible area. By Torah law, one who wants to transport an object within a reshut ha-rabim may carry it a bit less than four amot, stand still in order to establish a new location for the object, then walk again for less than four amot. He can continue in this way – starting and stopping – until he has transported the object wherever he wants it. However, the Sages forbade this lest one end up carrying more than four amot and thus violate Torah law.
I'm confused: theoretically, to transgress only the melacha derabanan and not mdeoraita, should one never stop at all (like the first source says) or should one stop every 4 tefachim (like the second source says)