Proof of proveit.linear_algebra.addition.norm_of_sum_of_orthogonal_pair theorem

import proveit
theory = proveit.Theory() # the theorem's theory

%proving norm_of_sum_of_orthogonal_pair

With these allowed/disallowed theorem/theory presumptions (e.g., to avoid circular dependencies), we begin our proof of
norm_of_sum_of_orthogonal_pair:
(see dependencies)