The INDEPENDENT-SET problem is a well-known NP complete problem that takes in a graph $G$ and an integer $k$. It returns true if $G$ has an independent set of size $k$.
An instance of the TFS (triangle-free-set) problem takes in a graph $G$ and an integer $k$ and it returns true iff $G$ has a subset of size $k$ whose induced subgraph is triangle free.
I want to perform a polynomial-time reduction of IS to an instance of triangle-free-set. So I start off with an instance of INDEPENDENT-SET, and I want to reduce it to an instance of TFS. But I'm not quite sure how to do this. I tried many things, like adding additional vertices for each pair of vertices, but I don't think this is right. I also saw a similar question here: NP Complete Proof - Polynomial Reduction, but I cannot quite figure out the approach from just that one person's question.
I would greatly appreciate any help.