Wednesday May 28

When does ab congruent to ac mod n imply b congruent to c mod n? Answer: if gcd(a,n)=1.
In general, we only learn b congruent to c mod n/gcd(a,n).

Def: the image of a function.
Theorem: every function factors as a surjection followed by an injection.
This was an existence statement; we made a uniqueness statement, which we'll prove next time.