suffices : a.norm = a.norm.natAbs
a b c : ℤω
⊢ ↑(norm a) = ↑(natAbs (norm a))
a b c : ℤω
this : norm a = ↑(natAbs (norm a))
⊢ ↑(norm a) = ↑(natAbs (norm a))

case this
a b c : ℤω
⊢ norm a = ↑(natAbs (norm a))