〜ている

〜ている is the single most overloaded form in Japanese, and the source of countless beginner errors. The progressive reading ("is doing X") is the textbook gloss for action verbs, but for change-of-state verbs (来る, 結婚する, 死ぬ, 知る) it instead marks the resulting state — 来ている means "has come / is here," not "is in the process of coming."

The rule of thumb: which reading you get depends on the verb's aspect class, not the construction.
• Activity verbs (run, eat, study) → progressive: 走っている = "is running."
• Change-of-state verbs (come, marry, die, know) → resulting state: 結婚している = "is married," not "is getting married."
• Some verbs allow both readings depending on context: 着る ("put on / wear").

A classic test case: 知る ("come to know"). 知っている = "know" (resulting state of having come to know). 知らない (plain negative) doesn't use ている because 〜ない negates the prior coming-to-know — "I don't know." 知っていない is rare and means "I haven't (yet) come to know."

The contracted 〜てる is the casual register form — identical meaning, just dropping the い.