The statement in present time, "The soldier lays aside his knapsack and lies down," becomes as a statement of a past act; as, "The soldier laid aside his knapsack and lay down"; "The hen has laid an egg"; "The egg has lain (too long) in the nest."
In poetic phraseology especially, the transitive lay (in all its tenses) is used reflexively as an equivalent of lie, lay, etc., as in the following examples:
learn, teach: Once learn was good English for teach, and signified both the imparting as well as the acquiring of knowledge. An example of this use may be found in Shakespeare (Romeo and Juliet) and the Book of Common Prayer, but general modern usage restricts learn to the acquiring and teach to the imparting of knowledge.
least: Grammatical writers have reason on their side in objecting to the use of a superlative for a comparative. "Of two evils choose the less," is better than "choose the least." A careful speaker will observe this form. See more and most.