Rif Pesachim 16b {Chagiga 22a continues; Pesachim 50a-b}

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16b

{Chagiga 22a continues}
he is pursuing a male, or a betrothed damsel {to sleep with} on Yom Kippur, and so it is permitted to save him {from sin} by {taking} his life, as we learn {tnan}, "And these we save by
{taking} his life..."

END PEREK THREE - (ve)Elu Ovrin

BEGIN PEREK FOUR - makom shenahagu
{Pesachim 50a}
Mishna:
In a place where they are accustomed to do work on erev Pesach until midday, we may do. In a place where they are accustomed not to do work on erev Pesach we do not do.
One who travels from a place where they do to a place where they do not do, or from a place where they do not do to a place where they do, we impose upon him the stringencies of the place from which he left and the place to which he is going.
{Pesachim 50b}
And one should not act differently, because of the dispute {which would ensue}.

Gemara:
Why did we have in the Mishna particularly erev Pesach? Erev Shabbat and erev Yom Tov as well!
For they learnt {in a brayta}: Anyone who performs work on erev Shabbat and erev Yom Tov, from mincha {=about 2 1/2 hours before nightfall} and on will never see a sign of blessing.
There, it was from mincha and on which is forbidden, but immediately before mincha it is permitted. Here, from midday.
Alternatively, there, it is a sign of blessing which he will not see, but we do not place him under the ban. Here, we would place him under the ban.

They learnt {in a brayta}: One who performs work on erev Shabbat and erev Yom Tov from mincha and on, and on motzaei Shabbat and on motzaei Yom Tov, and wherever there is the slightest suspicion of violation -- to include a public fast day -- he will never see a sign of blessing.

Rava opposed {two pesukim}: It is written {Tehillim 108:5}:

ה כִּי-גָדוֹל מֵעַל-שָׁמַיִם חַסְדֶּךָ; וְעַד-שְׁחָקִים אֲמִתֶּךָ.

5 For Thy mercy is great above the heavens, and Thy truth reacheth unto the skies.