Quote from: BrewMaster on Today at 02:07:34 AM

there is no special formula for point subtraction as far as i know. instead the P-Q is simply defined as P+(-Q) (same as addition) and -Q or negative of a point is defined as negating its y coordinate. or in other words -Q(x,y) = Q(x,-y) and since we don't use negative numbers in modular arithmetic -y becomes P-y where P is curve's prime.

oOO !! wonderfully explained, first test -> total success .. I understood the first time when research for several weeks had not led to much.
Many thanks to you BrewMaster (again ^^)
It is this notation (-y becomes P-y where P is curve's prime) that I have not seen anywhere that I am lacking.