theorem Th63:
  len nf s = 0 implies s = 1_FreeProduct(H)
proof
  assume len nf s = 0;
  then nf s = {};
  then A1: {} in s by Def7;
  consider x being Element of FreeAtoms(H)*+^+<0> such that
    A2: s = Class(EqCl ReductionRel H,x) by EQREL_1:36;
  thus s = Class(EqCl ReductionRel H,{}) by A1, A2, EQREL_1:23
    .= 1_FreeProduct(H) by Th45;
end;
