# File lib/eymiha/math3/point3.rb, line 178
    def subtract!(x=0,y=0,z=0)
      if x.kind_of? Numeric
        add!(-x, -y, -z)
      elsif x.point3_like?
        subtract! x.x, x.y, x.z
      else
        raise_no_conversion x
      end
    end