I wanted to renumber and better match the inline comment...how about

```
# (r0 + r1)**2 - (r2 + r3)**2
r0, r1, r2, r3 = rterms
s0, s1, s2, s3 = [r**2 for r in rterms]
eq = s0 + s1 + 2*r0*r1 - (s2 + s3 + 2*r2*r3)
```

or

```
def _sqnorm(a, b):
    return a**2 + b**2 + 2*a*b
...
r1, r2, r3, r4 = rterms
eq = _sqnorm(r1, r2) - _sqnorm(r3, r4)
...
r1, r2, r3 = rterms
eq = _sqnorm(r1, r2) - _sqnorm(r3, arg)
...
```