[.(PI / 4),((3 / 4) * PI).] c= ].0,PI.[ by Lm9, Lm10, XXREAL_2:def 12;
then cot | [.(PI / 4),((3 / 4) * PI).] is decreasing by Th8, RFUNCT_2:29;
hence (cot | [.(PI / 4),((3 / 4) * PI).]) | [.(PI / 4),((3 / 4) * PI).] is decreasing ; :: thesis: verum