reserve a,b,p,k,l,m,n,s,h,i,j,t,i1,i2 for natural Number;

theorem Th43:
  i-'i1>=1 or i-i1>=1 implies i-'i1+i1=i
proof
  assume i-'i1>=1 or i-i1>=1;
  then i-'i1+i1=i-i1+i1 by Th39
    .=i;
  hence thesis;
end;
