Given a field $K$ and an element $q \in K$ one can define the Hecke-Algebra $H_n(q)$ ($n \geq 2$) by the generators $1, g_1, ..., g_{n-1}$ and the relations
(1) ...
(2) ...
(3) $g_i ^2 = (1-q)g_i +q$, $1 \leq i \leq n-1$.
I do not understand how to interpret "$+q$" in the third relation: q is no element of the Hecke-Algebra, so how can we add it to $g_i$?