boolean aequal(S2Point that,double margin){
  return (Math.abs(x - that.x) < margin) && (Math.abs(y - that.y) < margin) && (Math.abs(z - that.z) < margin);
}

boolean aequal ( S2Point that , double margin ) { return ( Math . abs ( x - that . x ) < margin ) && ( Math . abs ( y - that . y ) < margin ) && ( Math . abs ( z - that . z ) < margin ) ; }
compare two vectors , return true if all their components are within a difference of margin .
