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 ler_piexpz2l x (x0 : 0 < x) (x1 : x < 1) :
{in >= 0 &, {mono (exprz x) : x y /~ x <= y}}.