Fact ler_wpeexpz2l x (x1 : 1 <= x) :
{in >= 0 &, {homo (exprz x) : x y / x <= y}}.
Fact ler_wneexpz2l x (x1 : 1 <= x) :
{in <= 0 &, {homo (exprz x) : x y / x <= y}}.

Lemma leq_add_dist  m1 m2 m3 : `|m1 - m3| <= `|m1 - m2| + `|m2 - m3|.