See ↑ IDEA 1
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• ↑ be lost/deep in thought
• ↑ break sb's train of thought
• ↑ don't give it another thought
• ↑ give sth a lot of thought
• ↑ give sth some thought
• ↑ have a thought
• ↑ I wouldn't have thought
• ↑ lose your train of thought
• ↑ school of thought