Day 9: mat385

• 2.1 homework returned: graded #4, 17, 35
  • 4: In every case, we need to ask "what assumptions are we making that are our own, and not actually specified?"

  • 17: if you start by assuming $x=2m$, and $y=x+1$, then you also need to assume $x=2m+1$ (or use Example 9, which one wily student did!).

    We could use induction for this proof, now.

  • #35: You really should use commutativity..., and start from the definitions of "perfect squares".

    What definitions and properties are you relying on?

• I did put the notes from last time on-line, and I'll continue that each day.

and we began section 2.4: Recursion.

We'll finish that up first.