theorem :: WAYBEL17:17

for S, T being non empty RelStr
for D being Subset of S
for f being Function of S,T st ( ( ex_inf_of D,S & ex_inf_of f .: D,T ) or ( S is complete & S is antisymmetric & T is complete & T is antisymmetric ) ) & f is monotone holds
f . (inf D) <= inf (f .: D)