I'm having trouble proving the implication rule for SD+

I need to show that:

L => M is equivalent to ~L v M.

I got the proof the other way around, this one is just bugging me.

Here is the kicker, I can only use the rules of SD, not SD+, which are the basic logical operator introduction and elimination rules.

I guess I would try to get ~L first and use Disjunction Introduction to get ~L v M.

The problem is getting ~L. I tried assuming L, but I'm having trouble finding a contradiction.

Any ideas??