reserve a,b,c,d,m,x,n,j,k,l for Nat,
  t,u,v,z for Integer,
  f,F for FinSequence of NAT;
reserve p,q,r,s for real number;

theorem
  n>0 & a>b & a,b are_coprime implies (a|^n+b|^n) gcd (a|^n -b|^n) <= 2
  proof
    assume n>0 & a>b & a,b are_coprime; then
    a|^n > b|^n & a|^n, b|^n are_coprime by Th40,WSIERP_1:11;
    hence thesis by Th8;
  end;
