Arguments real_ltr_normlP {x y}.

Lemma lerif_nmul x1 x2 y1 y2 C1 C2 :
y1 <= 0 -> y2 <= 0 -> x1 <= y1 ?= iff C1 -> x2 <= y2 ?= iff C2 ->
y1 * y2 <= x1 * x2 ?= iff (x1 * x2 == 0) || C1 && C2.