suffices h : a.norm = a.norm.natAbs
a b c : ℤα
⊢ ↑(norm a) = ↑(natAbs (norm a))
a b c : ℤα
h : norm a = ↑(natAbs (norm a))
⊢ ↑(norm a) = ↑(natAbs (norm a))

case h
a b c : ℤα
⊢ norm a = ↑(natAbs (norm a))