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alternately; in succession
「相」 has other readings with different meanings.
喜びと悲しみが相来た。
Joy and sadness came in turns.
成功と失敗を相経験してきた。
I've experienced successes and failures alternately.
笑いと涙が相入り混じる感動的な式だった。
It was a moving ceremony where laughter and tears alternated.