One way to define the Steenrod Operations is to use the cup-i product, as in Mosher and Tangora's book. It basically says, given the chain complex from mod-2 homology $C_*$, define $D_0 : C_\*\to C_\*\otimes C_\*$, so that the cup product is given (on cocycles) $(u\cup v)(\sigma) = (u\otimes v)(D_0\sigma)$ and then for higher $i$, define $D_i$ so that $D_{i-1}+\rho D_{i-1} = D_i\partial + \partial D_i$ where $\rho$ is the flipping map. Then the $\cup_i$ product is just $(u\cup_i u)(\sigma) = (u\otimes u)(D_i\sigma)$ And then define for $[u]\in H^n$ $Sq^{2n-i}([u]) = [u\cup_{i}u]$ This definition seems perfectly well-defined as a binary operation, and yet wherever I've seen it done it has only even been used as a unary operation. Is there a reason why this is the case, why either the product is undefined as a binary product or not useful as a binary product or just too hard to use? Is this a dumb question? Thanks, -Joseph