rosa.s could it be y= -|x| line shifted up one ish? Dunno if that was explained well, the first point going from right to left would be (0,1) then (-1,2) and (-2,3) just progressing like y= -|x| but only for positive values of y and negative x as in it'd be within the 2nd quadrant. I feel very wrong in that but it's what I would try, then I'd say I'm not sure but that's an educated guess...
If what I wrote makes no sense I could try re-explaining. I got |y|= -|x|+1