> A distance in space-time is now the square-root of minus the squares of the distances in each of the dimensions of space, plus c square times the squared distance in time.

In case anyone was having trouble parsing this, that's:

√(-(∆x² + ∆y² + ∆z²) + c²∆t²)

Or:

√(c²∆t² - ∆x² - ∆y² - ∆z²)