reserve i,j,k,n,m,l,s,t for Nat;
reserve a,b for Real;
reserve F for real-valued FinSequence;
reserve z for Complex;
reserve x,y for Complex;
reserve r,s,t for natural Number;

theorem Th49:
  n divides m implies n gcd m = n
proof
  set N = n gcd m;
  assume n divides m;
  then
A1: n divides N by NAT_D:def 5;
  N divides n by NAT_D:def 5;
  hence thesis by A1,NAT_D:5;
end;
