The next halving is expected to take place by the year 2020, during which the price increase is an assured as the ongoing demand for bitcoin will generate the decreased supply an increase in value. So for the Op I would like to suggest him buy when the price seems low, during halving the price will be increasing same as the recent price wave.
That's a common myth. The halving does not decrease the supply. The supply is always increasing until it reaches 21 million. You assume that the demand will continue to increase, but that is not guaranteed.
It is not a myth, it is just you nitpicking
Or rather deliberately misinterpreting the meaning of the term in the given context. Obviously, people mean the supply of new coins to the market which is evidently diminishing after the halving, as it is meant by the law of supply and demand (I wouldn't call that law a myth either), which people implicitly refer to here. What you mean is total supply of coins in circulation, but the distinction can be easily drawn from the context, and in this case specifically your comment is totally out of place and beside the point