How many RAW dependencies are present in these instructions?

What is the number of RAW dependencies in below set of instructions?

I1: R1 = R2 - R3 I2: R2 = R1 + R3 I3: R3 = R1 + R2 I4: R1 = R2 - R2 

I can see the following RAW dependencies in it:

$ I_2-I_1\ for\ R_1$ ……… (a)

$ I_3-I_1\ for\ R_1$ ……… (b)

$ I_3-I_2\ for\ R_2$ ……… (c)

$ I_4-I_2\ for\ R_2$ ……… (d)

I think taking (a) and (b) implies that (c) has already been included. So, should this be counted as 4 RAW dependencies or 3 RAW dependencies?

https://en.wikipedia.org/wiki/Hazard_(computer_architecture)#Read_after_write_(RAW)