"in X, **such that**..."

An associative function $f : X \\times X \\to X$ is a binary operation for all $~$x, y, z$in$X$,$f(x, f(y, z)) \= f(f(x, y), z)$~$\. For example, $+$ is an associative function, because $(x + y) + z \= x + (y + z)$ for all values of $x, y,$ and $z$\.

in X, such that…