Rif Shabbat 63b {Shabbat 149a continues ... 149b}

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63b

{Shabbat 149a continues}
according to him who says, Lest he erase, we do not fear; but according to him who says, Lest he read [secular documents], we do fear.

And the halacha is not like Rav Bibi {who said "lest he erase"} for he is in diagreement with Rabba, who said "One may not read by the light of a lamp {on Shabbat, lest he come to tilt the lamp} even if it is as high as twice a man's stature, even if it is as high as [the measurement of] two ox-goads, or even as ten houses on top of each other," and we establish the halacha like him {Rabba in this matter}.

And this that we learnt {in a brayta} - A man may count his guests - how many shall be within {=how many at the priveleged circle at the head of the table} and how many without and how many portions he is to set before them, from writing on a wall, but not from writing on a tablet or a board. And we establish this {brayta} as referring to a case in which it was engraved {on the wall, so that he cannot erase, and as for coming to read secular documents, we do not fear} for he will not come to switch from walls to documents. But if it was written {rather than engraved, on the wall} it is forbidden, whether high or low {on the wall}.

The learnt {in a brayta}: One must not look in a mirror on Shabbat. And Rabbi {our gemara: Meir; girsa difference perhaps a result of the following word matir} permits [one to look] in a mirror that is fixed to the wall.
And we conclude that we are dealing here with a metal mirror, and like the dictum of Rav Nachman citing Rabba bar Avuah, who said: Why was it ruled that a metal mirror is forbidden? Because a person {adam} usually removes straggling hairs with it, for it{s edge} is sharpened like a scalpel. {The tanna kamma making no distinction between affixed and non-affixed amongst metal mirrors}.
We thus deduce that a mirror not of metal is permitted, whether it is fixed to the wall or not fixed to the wall, and of metal, it is forbidden, like the Tanna Kamma, and even if it is fixed to the wall.

The Sages learnt {in a brayta}: The writing under a painting or an image {=the written legend beneath a picture} may not be read on Shabbat. And as for the image itself, one must not look at it even on weekdays, because it is said {Vayikra 19:4}:

ד אַל-תִּפְנוּ, אֶל-הָאֱלִילִם, וֵאלֹהֵי מַסֵּכָה, לֹא תַעֲשׂוּ לָכֶם: אֲנִי, ה אֱלֹקֵיכֶם.

4 Turn ye not unto the idols, nor make to yourselves molten gods: I am the LORD your God.

And what does it teach? Rav {our gemara: Rav Chanin} said: Turn not unto that conceived in your own minds.

{Note: Tosafot: the interdict is only against images made for idolatrous purposes, but others are permitted.}

"A MAN MAY CAST LOTS WITH HIS SONS...": {in order to see who gets what portion}
With his sons and household, yes, but with others {=strangers}, no.
What is the reason?
As Rav Yehuda cited Shmuel, for Rav Yehuda cited Shmuel: The members of a company who are particular with each other {in that each has his own food and if one takes from another, he keeps track} transgress [the prohibitions of] measure, weight, number, borrowing and repaying on Yom Tov,

{Shabbat 149b}
and according to Bet Hillel, also that of taking interest.