reserve a,b,c,k,m,n for Nat;
reserve i,j,x,y for Integer;
reserve p,q for Prime;
reserve r,s for Real;

theorem Th8:
  <=6n+1(n) c= Segm(6*n+2)
  proof
    let x be object;
    assume x in <=6n+1(n);
    then consider a such that
A1: x = a and
A2: a <= 6*n+1;
    a < 6*n+1+1 by A2,NAT_1:13;
    hence thesis by A1,NAT_1:44;
  end;
