Y by pavel kozlov
Initially, a pair of numbers
is written on the board. If for some
and
one of the pairs
and
is written on the board, then you can add the other one. Similarly for
and
. Prove that for each pair that appears on the board, its first number will be positive.







This post has been edited 2 times. Last edited by VicKmath7, Apr 19, 2022, 5:46 PM