Fact Pell_sym x y : Pell x y <-> Pell y x.

Theorem alpha_nat_2lm b n m l j v :
2 <= b
-> v = alpha_nat b (S (S m)) - alpha_nat b m
-> arem n (S m) l j
-> rem (alpha_nat b n) v = rem (alpha_nat b j) v
\/ rem (alpha_nat b n + alpha_nat b j) v = 0.