private Echo_Set(float gap = 0, Echo_Set next_e = null, int sn = 0, int en = 0)
{
this.gap = gap;
this.next_e = next_e;
this.sn = sn;
this.en = en;
}
private Send_Set(Echo_Set next = null, Send_Set next_s = null)
{
this.next = next;
this.next_s = next_s;
}
