static BasicLogicRule curryLHS_BasicLogicRule(BasicLogicRule rule) {
  if (rule == null) null;
  while licensed {
    O lhs = rule.lhs;
    if lhs is And(O a, O b) {
      BasicLogicRule r = rule;
      rule = new BasicLogicRule(a, curryLHS(new BasicLogicRule(b, rule.rhs)));
      rule.trail = r.trail;
    } else break;
  }
  ret rule;
}