Like any definitional argument, it depends on how you define the term.

the correct one is: decreasing and programmed inflation.

If we take into account the bitcoins lost forever, it is possible that it is deflationary.

No. But it's deflationary. Meaning that the rate of inflation is cut in half every halving. The next halving will be in April. From that point onwards each day approximately 450 new BTC will be mined. Now it is 900, because at this time each ten minutes 6,25 BTC are mined. It is also important to note that that schedule cannot really be changed. In particular other than with gold there cannot be more issuance when price rises.