Output gate of selective write in lstm cells

here Ot-1 = Ux(t-1) + Ws(t-2) + b

how O is the function of x and s(t-2). s(t-1) should be that na how is O becoming that function. till now we read that s(t-1) is a function of xt-1 and st-2. O should be a parameter right like W or U or b or c