It is not a nit it is fundamental, a•b•c is associativity, specifically operator associativity.

Rounding and eventual underflow in IEEE means an expression X•Y for any algebraic operation • produces, if finite, a result (X•Y)·( 1 + ß ) + µ where |µ| cannot exceed half the smallest gap between numbers in the destination’s format, and |ß| < 2^-N , and ß·µ = 0 . ( µ ≠ 0 only when Underflow occurs.)

And yes that is a binary relation only

a•b•c is really (a•b)•c assuming left operator associativity, one of the properties that IEEE doesn't have.