for X1, X2 being non empty set
for cB1 being filter_base of X1
for cB2 being filter_base of X2
for cF1 being Filter of X1
for cF2 being Filter of X2
for Y being non empty TopSpace
for x being Point of Y
for f being Function of [:X1,X2:],Y st x in lim_filter (f,<.cF1,cF2.)) & <.cB1.) = cF1 & <.cB2.) = cF2 holds
for V being Subset of Y st V is open & x in V holds
ex B1 being Element of cB1 ex B2 being Element of cB2 st f .: [:B1,B2:] c= V