IMO Shortlist 1967 problem 4
Dodao/la:
arhiva2. travnja 2012. A subset
of the set of integers 0 - 99 is said to have property
if it is impossible to fill a crossword-puzzle with 2 rows and 2 columns with numbers in
(0 is written as 00, 1 as 01, and so on). Determine the maximal number of elements in the set
with the property
%V0
A subset $S$ of the set of integers 0 - 99 is said to have property $A$ if it is impossible to fill a crossword-puzzle with 2 rows and 2 columns with numbers in $S$ (0 is written as 00, 1 as 01, and so on). Determine the maximal number of elements in the set $S$ with the property $A.$
Izvor: Međunarodna matematička olimpijada, shortlist 1967
Školjka 
