Dummy instructions to convert combine +- to Unity5

Hello
I do not know anything about shaders, but I am trying to use the gems package from Unity5, and upgrade it. Already found out how to replace the TexGen fixed function. No idea what that is, but it seems to be working.

Now, I have two lines, that look like this:

combine previous, previous +- texture

and

combine texture + previous, previous +- texture

I understand the problem are those +-, but I have no clue what that means or how to fix them. Ideas?
Best,
Alberto